spend...in doing 与 spend...on doing 都可以说，比较而言，前者比后面更常见，但总的说来，省略介词的用法最常见，即只说 spend...doing。

首先要强调的是，你的两个句子，语意是有区别的：

...on watching TV.  在看电视这个方面花了不少钱；

...in watching TV.  看电视的时候花了不少钱；

其次，国内（包括港澳台）很多英语老师在教学的时候，都认为 spend...doing sth 是doing前面省略了in：spend ... (in) doing sth. 但似乎很多母语者并不认同。

不过，介词无论被语法专家套上什么专业术语，装入什么语法规则，介词的实质含义是不会发生变化的，所以建议网友按照如下原则使用：... on activities / in enclosed spaces / at locations，在这个“友情提示”下，遇到动词，直接加ing即可。

一家之言，仅供参考；

勤查英英，必有所获！

spend...in doing与spend...on doing没有区别，可以互换使用。省略介词的用法最常见，即只说 spend...doing。

【注意】有些辅导资料指出：“spend...on后面不能接 doing，只能接something。”这种说法是错误的。

薄冰老师曾经就解答过类似问题，你可以看看，在“薄冰英语常见共性问题解答”一书第199页。我只引用一部分：

“spend作为及物动词时，后须接宾语（多指时间或金钱）如 “介 词 on+ 宾语 ”

或加“（介 词 in）+动 名 词 +宾 语 ”。如 ：

I spent a lot of money on books.

I spent a lot of money （in）buying books.

介 词 in 可省去。也可以用介词on代替in,但似乎比较少见。如 ：

I spent a lot of money on buying books.”

他举的是money的例子，下面我会举time的例子。

关于花费时间是用in doing sth还是用on doing sth抑或是省略in/on，可能有美式和英式的差别。柯林斯代表的英式现今似乎并不接受时间+in doing sth结构（注意大约在2000年前是接受的，老的语法书上都是有的），而美式似乎不忌讳这个，虽然也不多见，但照用，这个可以从纽约客和纽约时报上获悉。希望对你有帮助！

1.house-proud /'- -/adj liking to have everything in perfect

order in the house and spending a lot of time on keeping

it clean and tidy, perhaps too much so（朗文当代英语大辞典英英英汉双解house-proud词条下）

2.<young architects usually spend their first years in drafting plans rather than

in designing buildings>(Websters New Dictionary of Synonyms第743页)

3.Martin: Well, to be perfectly honest, no. I’ve never really had needed it up to now.

Tina: You really need to spend a few hours in studying this book, then, if you don't

mind. I’m sure it’ll explain you how the system works.（Advanced Language Practice2009第三版第180页）

4.Given all of the above, it may seem as if corpus linguists are supposed to

spend quite some time on learning a large number of sometimes quite

complex statistical tests.（The Cambridge Handbook of English Corpus Linguistics第71页）

5.The rest of the family spent their time in repeating malicious gossip about Eugénie's past life.（Longman Collocations Dictionary and Thesaurus2013第五版unkind词条下）

6.The Chief Executive of the company said that they had spent ten years on perfecting the product.（Longman Language Activator第二版585页）

7.They spend years in study and in acquiring degrees with a vague sense they are preparing for something, without actually leaping into what it is they might want to do.(纽约时报20170425)

8.Why do we spend time in demanding virtual worlds that mimic the monotony of our jobs?(The New Yorker2015年6月8日)

9.剑桥高阶第二版在解释take your time的时候是这么写的： said to mean that you can spend as

much time as you need in doing something, or that you should slow down，有in，可能是为了结构清晰的缘故。

10.Should we spend our time in prolonging misery when we believe that there is no chance of change?（Longman Language Activator第一版第796页）

11.Teachers ought to spend more time on teaching grammar.（A Comprehensive Descriptive Grammar of English by Declerck）

12.章振邦新编高级英语语法第419页：

“Mr Richardson's spent his life （in）  writing this book.

He spent the time ( in ) leafing through his program, looking for familiar names.

但是在spend的被动结构后，一般不可省略in：

The whole morning seemed to be spent in loading the car with a variety of bags, baskets and mysterious

parcels.”

 “被动结构后一般不可省略in”确实是这样，省略in的不多见，韦氏高阶上有一句是这样的，省略了in：

His months spent researching prison life gave him greater empathy towards/for convicts.

spend 后面接名词通常用on sth 接动词用(in可省略)doing sth

spend1 /spend/ ●●● S1 W1 verb (past tense and past participle spent /spent/)    

1 MONEY [intransitive, transitive] to use your money to pay for goods or services I can’t afford to spend any more money this week.spend £5/$10 etc I only want to spend about $20.spend something on something More money should be spent on education.spend something on somebody Mum never spends any money on herself. The repairs cost a lot, but it’s money well spent (=a sensible way of spending money)

Grammar You spend money on something:I don’t spend much on clothes.✗Don’t say: I don’t spend much for clothes.

2 TIME [transitive] to use time doing a particular thing or pass time in a particular place spend time etc with somebody I want to spend more time with my family.spend time etc in/at something We’ll have to spend the night in a hotel. His childhood was spent in Brazil.spend time etc doing something Stacey spends all her free time painting.

3a) spend the night with somebody to stay for the night and have sex with someoneb) spend the night (at something) if someone spends the night at someone’s house, they sleep at that person’s house for a night She spent the night at a friend’s house.

4 FORCE/EFFORT [transitive] to use effort or energy to do something I love to cook, but I don’t feel like spending the energy every evening.

5 → spend a pennyTHESAURUSspend to use money to buy thingsI bought two skirts and a T-shirt and I only spent $50.How much do you spend a week on food?go through something (also get through something British English) to spend all of an amount of money over a period of time – used especially when saying that someone spends a lot of moneyI got through all my money in less than a month, and had to get my parents to send me more.go to great expense to spend a lot of money in order to do something, because you think it is important or specialThe party was wonderful – they had obviously gone to great expense.There’s no need to go to great expense.squander /ˈskwɒndə $ ˈskwɑːndər/ to waste money on unnecessary things, instead of saving it or using it carefullyHis son had squandered the family fortune on gambling and women.splash out British English informal to spend a lot of money on something you really want or will enjoyLet’s splash out on a bottle of champagne.People often splash out for Christmas and then regret it later.blow informal to spend a lot of money on something, especially on something that you do not really needHer husband blew all their savings on a new sports car.economize to spend less moneyWe’re trying to economize by eating at home instead of going out for meals.→ See Verb tableExamples from the Corpusspend• I bought two skirts and a T-shirt and I only spent $50.• During the recession, even the tourists weren't spending.• We spent a lot of energy looking for a nice apartment.• We spend about £85 a week on food.• At seventeen, he announces that he wants to spend his whole life in a ruined castle by the sea.• Dani spends hours on the phone.• Everyone spends more at Christmas - it's an important time for business.• The government has promised to spend more money on education.• All travelers apparently will be spending more time outdoors this summer.• She spends most of her salary on clothes.• Mom spent most of the weekend cleaning up the house.• Reagan and Gorbachev spent nine hours and forty-eight minutes in face-to-face negotiations.• Customers receive additional Clubcard points for every £2 spent on a Tesco Credit card.• Children are particularly at risk because of the amount of time they spend out of doors.• Now they spend quite a bit of their money, which is nice.• They spend quite a lot of money each week on eating out.• We spent the week in a dingy motel off Route 9.• He spent the whole morning reading the report.• A diabetic, she spent two days in the hospital last week when stress sent her blood pressurerocketing.• I never seem to have any time to spend with the children.