1. 下面两句相等（现在分词可以用完成式和一般式），是个特例：

Having finished his work, he began to have dinner.

=Finishing his work, he began to have dinner.

因为动词finish表示完成，它的意思是：做完工作后，他就开始吃饭。

2. 假若将上面一句中的动词finish改为do，就不可以了。如：

正常：Having done his work, he began to have dinner.

不妥：Doing his work, he began to have dinner.

因为误句的意思是do为持续性动词，句子终的感觉好像是do与begin to have dinner是同时发生的。

3. 下面这个句子：

Having found a hotel, we looked for somewhere to have dinner.

句意为：在找好旅馆之后，我们就去找吃饭的地方。

如果将句子中的现在分词完成式having found换成一般式finding，不能算错：

Finding a hotel, we looked for somewhere to have dinner.

由于句中的find为终止性动词，若用一般式，说明两个动作是前后紧挨着的动作，即一找到宾馆就去找吃饭的地方（给人感觉有饿得不行的意味）。

类似的例子如：

Hearing the news, they all jumped for joy. 听了这消息他们都高兴得跳了起来。

Taking a key out of his pocket, he opened the door. 他从口袋里掏出钥匙把门打开。

Turning around, she saw an ambulance driving up. 她转过身，看见一辆救护车开了过来。