Abstract: In the arid and semi-arid climate zone of the Qinghai-Tibet Plateau, the Rencuo Lake group, as an important part of the third pole of the Earth, plays a crucial role in understanding lake evolution due to its hydrochemical characteristics and isotopic studies. This research conducted 27 sets of water sample collections in the depression basin on the northwestern slope of the Nyainqêntanglha Range in Bange County, Naqu City, Tibet Autonomous Region. Using methods such as Gibbs diagrams, Piper diagrams, and hydrogen and oxygen isotope analyses, the hydrochemical characteristics and controlling factors of the Rencuo Lake group and its surrounding groundwater were thoroughly investigated. The results show that the pH values of the lake waters and groundwater generally range from 8 to 10, with the highest pH in the saline lakes, and the mineralization degree of the eastern lakes is generally lower than that of the western lakes. The contents of major ions such as K⁺, Na⁺, Mg²⁺, Cl⁻, SO₄²⁻, and HCO₃⁻ exhibit significant positive correlations with mineralization. The western lakes are primarily controlled by evaporation-crystallization processes, while the eastern groundwater and Jiuru Co are mainly controlled by rock weathering. The hydrogen and oxygen isotope analyses indicate significant evaporation effects in all lake waters. Jiuru Co is replenished by ice and snow meltwater and surface water, with groundwater seepage discharge, while Rencuo Yoma and Biga Co are respectively supplied by groundwater seepage from Jiuru Co and northern descending springs.