Bankog Co is located in the cold, arid-semi-arid monsoon climate zone of the northern Tibetan Plateau and is highly sensitive to climatic fluctuations. This paper selects 11 scenes of remote sensing images covering Bankog Co, vectorizes the lake boundaries, and establishes a dataset of the lake surface area from 1976 to 2024. In addition, data on the annual average maximum temperature, annual average minimum temperature, annual average temperature, and annual precipitation from the Bankog Meteorological Station for the years 1976–2023 were collected. The study shows that (1) between 1976 and 2024, the area of Bankog Co showed a trend of increase. In 1796, Bankog Co had its smallest area at 41.40 km2. By 2024, the area had increased to 138.53 km2, which is 3.3 times the size in 1976. During this period, the average expansion rate of Bankog Co was 2 km2/year. (2) The climate of Bankog Co is shifting towards a warmer and wetter direction, characterized by rising temperatures, a slight increase in precipitation, and a decrease in evaporation. (3) The expansion of Bankog Co is primarily influenced by climate change. Global warming has led to rising temperatures in the Tibetan Plateau, which in turn has accelerated the melting of glaciers and permafrost. The melting of glaciers and permafrost around Bankog Co results in a significant influx of meltwater into the lake, increasing its water volume and causing the lake’s surface area to expand. Additionally, increased precipitation and decreased evaporation both contribute to the rise in the lake’s water level. Meanwhile, geological structure, human activities, and recharge and discharge areas also have some impact on the changes in Bankog Co, but their effect is relatively minor compared to natural factors.