The alpine ecosystem of the Source Region of the Yellow River (SRYR) has a significant water conservation function which represents water cycle within the atmosphere and biosphere. In this paper, ecosystem water conservation (EWC) was modeled by a modified dynamic vegetation model. Based on water balance method, the spatial- temporal changes in EWC and the impacts of climatic change were analyzed in the SRYR during the period 1981- 2010. Results indicated that the EWC has a slightly decreasing trend of -1.15 mm/a in the past three decades. Furthermore, the EWC of most regions decreased especially in the southeast of the SRYR. In general, changes in both precipitation and atmospheric moisture demands have explicit influences on the amount and changes of the EWC, and the influences are various in different moisture conditions. In the southeast of the SRYR with sub- humid climate, both decreased precipitation and increased potential evapotranspiration induce the significant negative changes in the EWC. Meanwhile, in the northern part with semi- arid climate, increased precipitation is the main climatic factor leading the EWC to increase.