The water balance of lakes in the plain areas is difficult to estimate due to the influences of human activities.In the paper,a distributed hydrological model was constructed and the water balance was calculated for the Wolong Lake,an inland lake in the plain area.The model simulation results had a Nash coefficient being greater than 0.75 and a relative runoff error of being less than 3%. The water balance was further investigated for typical years,such as,wet year,normal year,dry year and extreme dry year.The results showed that under natural conditions,the lake storage were 20442 million m3、7911 million m3、1655 million m3、 6.87 million m3,respectively.If water was interrupted in the upstream section,the lake storage would reduce to 15424 million m3 for wet year,and to 1943 million m3 for the normal year.Under the dry year and the extreme dry year,there was no flow in the East and West Malian River,causing the lake to be extremely drought.