Worse than raining cats and dogs is hailing taxis. The phrase has a good rhythm to it. It just sounds good.

so that's to say,when the rain pours down ,dogs and cats drown ,so you recall heavy rain of the died body of the cats and dogs,doesn't it right?

The phrase raining cats and dogs is of unknown origin. A number of folk tales have been put forward to explain the phrase, for example, In 16th century Europe when peasant homes were commonly thatched, the home was constructed in such a manner that animals could crawl into the thatch and find shelter from the elements, and would fall out during heavy rain.