There are numerous lakes and reservoirs in the Lake Poyang basin. As the largest inflowing reservoir, Lake Zhelin serves as the largest regulating reservoir in the Lake Poyang basin.Lake Zhelin has a certain influence on the runoff into Lake Poyang.It can provide water flow to Lake Poyang during dry seasons and reduce the water flow during wet seasons.This paper focused on Lake Zhelin by discussing its formation and its water ecological environment changes.Then, Lake Zhelin's water environment changes in the past 30 years and the key driving factors of environmental evolution were analyzed.Results showed that Lake Zhelin's aquatic biodiversity decreased and water environment deteriorated but exhibited a recovery.The driving factors were the growing population in the watershed, leading to a higher pollution loading into the lake in recent years.This situation became worse due to further man-made destruction on the lake district ecological security barrier, unsustainable use and over exploitation of resources.Only by resolving the relationship between people and lake and taking reasonable measures to carry out integration research and comprehensive treatment, Lake Zhelin's water environment can be improved effectively and play its role in protecting Lake Poyang.