The Yarlung Zangbo River Basin,a typical area characterized by ecological fragility and sensitivity to environmental changes,boasts diverse vegetation and plentiful water energy resources. Water retention is an important function of ecosystem services. It is important to study the spatial-temporal distribution characteristics and influencing factors of water retention for the water protection,development,utilization and comprehensive management of water resources in the region. However,previous studies have mostly focused on the runoff response within the river basin,neglecting the water retention capacity of various ecosystem types within it and the contribution of different water budget variables to retention function. To accurately quantify the water retention capacity of different ecosystems,this study verified the applicability of the VIC model in the Yarlung Zangbo River Basin and quantified changes in water budget variables. It quantitatively evaluated and analyzed the changes in the water retention capacity of the ecosystem over the past 35 years,compared the water retention capacity in the basin according to different ecosystem types,and included water variables in the driving factors combined with the geographic detector index to identify the contribution of factors. The results show that: (1) The study area's climate conditions exhibit trends of warming and increasing humidity. During the 35 years,precipitation increased at a rate of 7.01 mm/10a,and vegetation evapotranspiration and surface runoff depth increased at rates of 6.15 mm/10a and 4.81 mm/10a,respectively. However,there was no obvious trend in groundwater runoff,vegetation interception,and soil moisture. (2) From 1980 to 2015,the water retention capacity of the basin exhibited a yearly decreasing trend,changing at a rate of -0.02 billion m³/a. The upper,middle and lower reaches conserved 7.175 billion,8.101 billion and 8.242 billion m³ of water,respectively,and the entire basin could conserve an average of about 23.518 billion m³ of water. (3) The geographic detector results indicate that increases in precipitation and evapotranspiration are the primary factors influencing water retention fluctuations in the region,contributing to the overall decline in the Yarlung Zangbo River's water retention capacity. The above changes in the water retention capacity of the ecosystem indicate a decrease in the water support function of vegetation in ecologically sensitive and fragile areas,which should be taken seriously in regional ecological restoration.