Urban lakes plays an important part of the urban ecological environment.In recent years，with the increase of population and the intensive human activities，a large number of urban lakes appear eutrophication and other water problems.This paper takes Qingshan lake，the largest inner lake in the core city of Poyang lake area，Nanchang，as the research object，explores its water quality status and change trend，and give some suggestion on how to control the pollution.Research shows that：（1）the Qingshan lake water quality status is given priority to with Ⅳ，Ⅴ water；the water quality index changed greatly with time and was affected by the environment. （2）The water quality changed significantly during the year，and the water quality was worse in summer and autumn than in winter and spring.（3）The annual variation of water quality is relatively large，and the year with a poor quality is 2008 and 2014 to 2015，the overall water quality shows an improvement trend in recent ten years，but the eutrophication index has a rebound trend in the past two years，which is worth noting. （4）The pollution sources are mainly urban rain sewage runoff and water pollution from the Yudai river，which can be treated by engineering，biological and source pollution.This paper studies the water quality of Qingshan lake to provide technical support for the ecological environment protection of urban lake water.