The main water supply source and the regularity of flow discharge influenced by tide in Dianshan Lake are discussed,to study the water balance during years of drought on the basis of the hydrometerologic data measured in 1988.Acoording to the result,it makes clear that all though rainfall was scarce in Dianshan Lake basin in 1988.the lake water still reached to its balance, because of the water supply by the neighboring rivers and lakes and the Changjiang River.It is suggested that succesive hydrometerologic data should be gathered for making full and rational use of Dianshan Lake, water resources.