同意曹老师的分析。

with 的宾语those born after 1980， 还可以再分：born after 1980 作those 的定语。

China's floating population contains many young people with those born after 1980 accounting for 56.5% of the total.  中国流动人口中年轻人较多，80后占总流动人口的56.5%。

with 开始后半句看不清结构了，是with 复合结构吗？

解答如下：

以上为：with+名词+过去分词“复合结构/with的独立主格结构）

With the experiments carried out ,we started new studies.

实验一做完，我们就开始心得研究。（表时间）

With my sister gone, there was nobody to help the old woman.

我姐姐一走，就没有人帮助那位老大娘了。（表原因）

The old gentleman was walking, with his arms folded across his chest.

那位老人在散步，双臂交叉放在胸前。（表方式）

Henry left the classroom, without a word spoken.

亨利一句话也没有说就离开了教室。（表伴随）

with的复合结构主要以以下几种形式出现在句子中，并在句子作状语成分。

 【一】With + 名词+现在分词

She stood on the top of the hill with her hair flowing in the breeze.

她站在小山顶上，长发在微风中飘拂。

 I was about to declare myself here in Southampton with trains  rattling overhead.

在南安普敦，火车在我上面的铁轨上隆隆作响，我就要表明我自己的身份，开始拉琴卖艺了。

With economy recovering, people’s living standard is improving.

随着经济的复苏，人民的生活水平也在改善。

【二】With +名词+过去分词

  They left with most of their work undone.

大部分的工作还没有做他们就离开了。

The year 2000 ended with nothing settled. 

2000年过去了，什么也没有解决。

The prisoner was brought in with his hands tied and feet chained. 

囚犯被带进来，手被捆着，脚被锁链锁着。

The shopping bag ladies wear layers of clothes, with newspapers 

stuffed between the layers as further protection against cold.

流浪女穿着一层层的衣服，层与层之间还塞满了报纸来进一步抵御严寒。

【三】 With+名词+不定式短语

With a lot of work to do, I don’t know whether I have time to go to the concert with you.

有这么多的工作要做，我不知道是否有时间和你一起去听音乐会。

  I really did not have time to relax with so many small children to  look after.

有很多的小孩儿要照顾，我真的没有时间去放松一下。

 I can’t go out with a lot of dishes to wash。

有这么多的盘子要洗，我出不去。

【四】With+名词+介词短语

He stood on a big rock with his face towards the rough sea.

他站在一块儿大岩石上，面朝着波涛汹涌的大海。

They stood with their arms round each other.

他们站在那里，相互拥抱着。

 His wife came down the stairs, with her one-year-old son in her arms. 

他 的妻子走下楼来，怀里抱着她那个一岁的儿子。

 【五】 With+名词+形容词

Even in winter he still slept with the window open.　

即使在冬天，他仍然开着窗户睡觉。

With chairman of the board seriously ill, we had to cancel the meeting.

由于董事长病的很严重，所以我们只好取消了这次会议。

With the weather unbearably hot, we had to have our air-conditioner working all the time。

由于天气热得令人难以忍受，所以我们只得一直开着空调。

【六】With+名词+副词

With two people away ill, we’ll have to close the office this afternoon.

由于两人有病没来，今天下午我们不得不停止办公。

 Her three children lay on the bed with all their clothes on.

她的三个孩子穿着衣服躺床上。

The child was free to do everything with her mother not in. 

母亲没在家，这个孩子可以自由地做一切事情。