In recent years, Dianchi Lake has become one of the national key treatment project, and one of the three most polluted rivers and three lakes for it''s increasing eutrophication, declining in water quality and water shortage. The water quality closely related to the water level of the lake. In this article, the main factors, which affect the water level, were preliminary studied based on the analysis of the water level changing trends from 1970to 2010at Haigeng station by using Mann-Kendall, one of nonparametric test methods. The results showed that Dianchi lake water level has been rising significantly since 1989, which is caused mainly by evaporation, siltation and human activities, rather than rainfall.