Abstract: A comprehensive understanding of the hydrological processes of thermokarst lakes on a seasonal scale is key to evaluating their environmental effects. In this study, a typical thermokarst lake was selected on the Qinghai-Tibet Plateau (QTP) and the meteorological and hydrological parameters were measured and calculated (2018—2020 to analyze the hydrological characteristics and environmental effects. The following results were obtained : ① Rainfall in spring recharges thermokarst lake water quickly and elevates lake water level rapidly; a power function was exhibited between lake water storage and water levels. ② The average annual lake evaporation and lake ice sublimation were 738 mm and 198 mm, respectively. Under the influence of rising air temperature, lake evaporation and ice sublimation may be increased in the future.③ The ionic concentrations in lake water exhibited a high value in the initial and later periods of the warm season, and the self-purification of lake ice and geochemical processes resulted in different ion migration mechanisms. The hydrological elements exhibited obvious seasonal variation characteristics owing to the effect of local factors. Moreover, the hydrological processes involving thermokarst lake evolution can cause permafrost degradation, lakeshore collapse and receding, water environment deterioration, greenhouse gases release, soil salinization, and vegetation degradation. Thus, the environmental effects of thermokarst lakes should be evaluated on the entire QTP in future studies.