The Yamzho Lake is the largest closed inland lake at the north foot of Mt.Himalayas,with a drainage area of 6100 km2.The lake covers an area of 621 km2 with an altitude of 4440 meters and a storage capacity of 16 billion m3.Precipitation is the main recharge source of the lake.Melt water makes up only 16 percent of the total recharge.Yearly lake level variation is within 0.6 meter.Due to self-regulation the highest water level of the lake does not appear in July or August when the rainfall is plentiful but in September or October.In a rainy year the lake level exhibits periodic variations and in a dry year the lake level has a fall tendency.The lake water level variation was influenced by temperature in the past 30 years.The analysis of the data for the last one hundred years shows that there is a tendency of lake level fall, the fall rate is 0.6meter/100 year.