Abstract: To solve the contradiction between the development of large areas of urban Greenland and scarcity of land and water resources for Greenland in Beijing, the implementation of green-roof vegetation is important. In this paper, the typical green-roof plant (E.japonicus) as the research object, the physiological response, landscape function and ecological serves function of E.japonicus were analyzed with the pot experiments in 4 different treatments of full irrigation (CK) (90%-100%FC), low water stress (LWS) (75%-85%FC), moderate water stress (MWS) (65%-75%FC), and serious water stress (SWS) (50%-60%FC) treatments. The results showed that the photosynthetic rate, transpiration rate, stomatal conductance and water use efficiency of E.japonicus was LWS>MWS>SWS respectively in three treatments of water stress. The difference of the photosynthetic rate, transpiration rate, leaf area, stomatal conductance, chlorophyll content and water use efficiency between CK and LWS was around 5%. In terms of ecological serves function there is no big differences for carbon fixation and oxygen release, and cooling and humidity of E.japonicus under different soil moisture levels. The LWS(75%-85%FC) stimulated the growth of E.japonicus, and effectively regulated the ?distribution of the?assimilation. Therefore, LWS (75%-85%FC) is the optimal water-saving irrigation model.