Abstract: Hydropower project not only benefits human society by regulating water supply,but also directly affects the natural hydrological regime of a river and ecosystem in river channels. For the sustainable development of both human society and ecosystem,it is necessary to achieve the balance between the water supply from the reservoir and water demands from both human society and relevant natural ecosystems.In this study,the influence of Pangduo Reservoir on hydrological regime in the Lhasa River Basin is investigated. Daily reservoir inflow,regulated outflow and reservoir storage in 2014-2020 are used to evaluate the effects of the reservoir operation through the Range of Variability Approach（RVA）. In total,32 flow indices that cover the flow magnitude,timing,frequency and duration which represent the full hydrological regime are designed and examined for the reservoir operation impacts in the Lhasa River. To better preserve the temporal continuity in the occurrence of extreme events,vector analysis is adopted. Results show that the Pangduo Reservoir has affected the overall hydrological regime in the Lhasa River to a medium level. The effects are especially serious in extreme low flow events that occur in winter and spring. Specifically,average flow in January,March and May,annual 1-day minimum flow,annual consecutive 30-day minimum flow,and the timing of the annual 1-day minimum flow increases and has reached a change degree of 100% according to the RVA standard. The overall alteration in the hydrological regime by the reservoir reached a degree of 62.21 % during 2014-2020,a moderate level by the RVA standard. In general,the Pangduo reservoir operation increased low flow but reduced high flow,which is common for reservoir operation. What is special for the Pangduo Reservoir, however, is its effects on low flows which are more severe than on high flows. The study demonstrates that the Pangduo Reservoir operation will perhaps result in a detrimental effect on river ecosystems if the current regulation continues. Although the major goal of the Pangduo Reservoir operation is to meet the demands from agriculture and municipality for social and economic developments,it should also seriously take the health of the Lhasa River ecosystems into consideration during the operation to strike a balance between the human and nature’s needs in the future. This study provides a timely assessment of the Pangduo Reservoir operation which will benefit future water resource management operation in the Lhasa River Basin.