In this study, the variation in area of Peiku Tso in Tibet is investigated, mainly based on the topographic map in 1975, nineteen scenes of Landsat (MSS, TM, ETM⁺) satellite images beginning the late 1970s through 2013, ICESat satellite data during the period of 2003 to 2009, along with 43 years of meteorological data near the lake. Results show that the lake area experienced a decreasing trend, so did the elevation of lake. In particular, the area was reduced by 10.68 km² (3.79%) during the period of 1975-2013. The spatial pattern concerning the times series of lake area maps indicates that the region with striking changes is located in the southern and the northeast part of Peiku Tso, where the water body shrinks toward north and southwest, respectively. Similarly, both the elevation and area of Peiku Tso exhibited a decreasing trend during the 2003-2009 years, respectively decreasing 0.17 m,4.4 km². The annual mean temperature exhibited upward trend and the mean annual precipitation saw downward trend in the watershed of Peiku Tso during the last 40 years. The precipitation was positively related to the shrinkage of lake area, but negatively to the temperature. Therefore, we infer that the decreasing precipitation is likely to be the main factor of the lake shrinking. Considering the variation of the glaciers, the supply function of their melt water to the lake is not evident though the variation of the glaciers in the above basin exhibited degrading status as glaciers in other regions of the Tibetan Plateau.