AbstractThe investigation on fish and their habitats in Hanjiang River system and Jialingjiang River system in west region of Qinling Mountains indicated that human activities had a great impact on fish diversity. This paper intended to give a general report and analysed the causes of the descent of fish diversity in this area. There were 142 species of fish recorded in these two river systems in Qinling Mountains ,but only 34 species were collected in this expedition to west region of Qinling. It was discovered that decrease of the number of fish species was caused by a lot of factors , including water conservancy facilities construction ,water pollution , over-fishing and illegal fishery.