The water level data of lakes, as an important indicator for evaluating changes in lakes, are of great significance for studying regional water resources changes and ecological environment conditions. However, most of the plateau lakes are located at high altitudes where population are sparse and natural conditions are harsh, and it is often difficult to obtain basic observation data. Based on satellite altimetry data and remote sensing image data, we obtained the water level and area data of Kusai Lake from 2008 to 2018, and analyzed the causes of water level change in association with meteorological data. Results manifested that the water level of Kusai Lake had gone through three stages from slow rise (2008-2011) to sharp rise (2011), and then to stabilization (2012-2018). The slow rise in the 2008-2011 stage was mainly triggered by warming and humidification of climate; the sharp rise stage in 2011 was caused by overflow in the upstream of Zhuonai Lake; in the 2012-2018 stage, the water level began to stabilize due to overflow in the Kusai Lake after receiving a large amount of incoming water and hence integrating with the upstream and downstream lakes in series. Correlation analysis of water level data and meteorological characteristic factors showed good correlation between lake level and changes in meteorological factors, and preliminary analysis suggested that the increase in regional precipitation was the main reason for the rise in water level of Kusai Lake, while the increase in glacial meltwater and permafrost moisture release caused by climate warming might be secondary causes.