Lakes on the Tibetan Plateau play critical roles in the water cycle of the ecological and environmental systems of the plateau. The Tangra Yutso is one of the largest lakes in the Tibetan Plateau. There was rare analysis on the change in the Tangra Yutso lake area, particularly a long-time series analysis.This study analyzed the Tangra Yutso lake area change using the RS and GIS techniques, which were combined with the meteorological station element, environment factors such as glacier, to explore the reasons of lake area change in the past 40 years.The results showed that mean lake area is 835.75 km² in 1977-2014, with the smallest lake area of 822.92 km² in 1990. The lake area increased from 829.15 km² in the 1970s to 827.50 km² in the 1980s, and then 826.42 km² in 1990s, respectivly. There was an increasing trend since 2000. The spatial variations of lake area are characterized by an increasing trend over the period of 1977-2014, particularly in the eastern and southern part of the lake, and the western small lake besides the Tangra Yutso is enlarged since September, 2014,and almost linked with the Tangra Yutso. The main reasons for lake change should be attributed to the melting of glaciers, snow cover and the increasing of precipitation caused by climate warming in the past 40 years.