Abstract: Based on the study on the data from observing and measuring between 1975 and 2004 for the Wolong Lake, the historical evolution of the wetland is analyzed. The water table changing trend of the Wolong Lake in the 29 years and the causes of the drop-off are studies. The water balance in the lake area is calculated according to the fundamental situation and monitoring data of the Wolong Lake wetland and its catchments area. It is proved that the water table drop-off and the water volume reducing in the lake for approximately three decades are resulted from the natural factors and man-induced factors such as climate, hydrology and so on.