Abstract: Rivers are the main channels connecting the ocean ecosystem and the inland ecosystem, and are also the major participants in the carbon cycle.The hydrochemical characteristics and carbon sink process in the Yarlung Zangbo River Basin were studied by the hydrochemical and elemental geochemical methods.The results showed that:(1) The average value of Total Dissolved Solid(TDS) of the Yarlung Zangbo River was 205.3 mg/L,which was higher than the average value of world's rivers; the HCO-3 and Ca2+ were the most abundant anion and cation of the river water respectively.(2) The mass balance model indicated that the chemical composition of the basin water was dominated by the weathering of carbonate rock with an average contribution of 56%,and by weathering of silicate rock and evaporated rock with an average contribution of 23% and 17% respectively; atmospheric precipitation input contributed to the main ion composition only by 3%.(3) The weathering rate of rock in the basin was 42.03 t/(km2·a),which was approximately twice of the average weathering rate of rock in the world's rivers.The rate of rock weathering in the flood season(72.00 t/(km2·a)) was much more influenced by the runoff than in the dry season(12.06 t/(km2·a)).(4) The rate of CO2 consumption from rock weathering in the basin was 407.13×103 mol/(km2·a),which was much higher than the average of the world's rivers.Among these, the average CO2 consumption rate of carbonate weathering was 232.29×103 mol/(km2·a),and the average CO2 consumption rate of silicate rock weathering was 174.84×103 mol/(km2·a).