The variation in water budget of closed lakes serves as an ideal research subject for studying lake responses to climate change. However，most existing studies focus on the long-term water volume changes of lakes on Qinghai-Xizang Plateau. Due to data scarcity，the intra-annual dynamics of water budgets and the contributions of balance components in these lakes remain unclear，hindering research on water budget dynamics and cli‐ mate change responses. Base on hydrological-meteorological observation data，reanalysis datasets，water balance equations，and inflow runoff calculation methods，this study analyzes the dynamic characteristics of water balance components［lake surface precipitation（P），inflow runoff（Rs），lake surface evaporation（E）］，lake level（H）and lake level difference（ΔH））in Bamu Co during the 2021-2023 monsoon periods；the relative contributions rates of water balance factors in different months and years；along with the interannual variations in meteorological elements including air temperature，downward radiation，and relative humidity. The results show that：（1）The water budget of Bamu Co exhibits significant interannual variation. In 2021，abundant P and Rs drove in H. In 2022，sharp declines in P and Rs led to a drop in H. In 2023，increases in P and Rs offset the intensified E，resulting in another rise in H.（2）ΔH is mainly regulated by Rs and E. On the monthly scale，the contribution of R s displays a “V”-shaped，while E shows an opposite trend. On the interannual scale，Rs plays a dominant role in positive variations（2021 and 2023），whereas E dominates negative variations（2022）.（3）Meteorological elements influenced ΔH through P-E balance adjustments：moderate temperature，high humidity，and medium radiation in 2021 maintained medium E/P ratio with positive ΔH（+231 mm）；elevated temperature，reduced humidity，and enhanced radiation in 2022 increased E/P ratio alongside decreased P and Rs，resulting in negative ΔH（-75 mm）；improved meteorological conditions in 2023 reduced E/P ratio and restored hydrothermal conditions，driving positive ΔH（+350. 6 mm）. This study provides crucial insights into unique hydrological mechanisms of monsoon-influenced lakes，supports ecological security barrier construction for the "Asian Water Tower"，and promotes sustainable development on the Qinghai-Xizang Plateau.