The paper emphasized the relationship between environment and water taking ecological demand water (EWD) in the Qaidam Basin─an inner basin in northwestern China, as a key issue to discuss based on landscape umpping. First of all. the spatial heterogeneity of ecosystem can be reflected well by landscape pattern; secondly, landscape patterns adjust closely with environmental changes; finally, water condition is the key ecological factor for landscape pattern in the arid region.The landsat TM image of 1:100,000 on September 22, 1996 were calibrated with topographical map of the same scale, and then landscape patterns were interpreted and mapped. As a result the Qaidam Basin could be divided into 14 main types, including 67 subtypes. Concerning the characteristics of the EWD of each sub-type, the EWD in the whole basin could be estimated according to the following formula:V= (E - P ) * S = r (KEo - P ) * S Where, V is the ecological demand for Water (m3), E is the evaporation potential on terrestrial surface (m). P is the precipitation in landscape unit (m), S is the area of landscape unit (m2), Eo is the evaporation potential on water surface (m), K is the evaporation coefficient, and r is the coverage.According to the results, the ecological demand for water of desert vegetation is about 9,65×108m3, while it is about 24.48×108m3 for the lake in the inner basin. Therefore, the total EWD occupies approximately 65.7％ of the total water resources in the basin. In conclusion, the quantitative method based on landscape ecological mapping is feasible, which attentively transfers the “point”information to the “area”. However, the preliminary results are expccted to improve by further field delta. The paper emphasized the relationship between environment and water taking ecological demand water (EWD) in the Qaidam Basin─an inner basin in northwestern China, as a key issue to discuss based on landscape umpping. First of all. The spatial heterogeneity of ecosystem can be reflected well by landscape pattern; secondly, landscape patterns adjust closely with environmental changes; finally, water condition is the key ecological factor for landscape pattern in the arid region. landsat TM image of 1: 100,000 on September 22, 1996 were calibrated with topographical map of the same scale, and then landscape patterns were interpreted and mapped. As a result of the Qaidam Basin could be divided into 14 main types, including 67 subtypes. Concerning the characteristics of the EWD of each sub-type, the EWD in the whole V = (E - P) * S = r (KEo - P) * S Where, V is the ecological demand for Water (m3), E is the evaporation potential On terrestrial surface (m). P is the precipitation in landscape unit (m), S is the area of ​​landscape unit (m2), Eo is the evaporation potential on water surface (m), K is the evaporation coefficient, and r is the coverage. According to the results, the ecological demand for water of desert vegetation is about 9,65 × 108m3, while it is about 24.48 × 108m3 for the lake in the inner basin. Thus, the total EWD occupies approximately 65.7% of the total water resources in the basin. In conclusion, the quantitative method based on landscape ecological mapping is feasible, which attentively transfers the “point ” information to the “area ”. However, the preliminary results are expccted to improve by further field delta.