Usually the calculation of eco-environmental water requirement (EWR) is based on the status quo of ecosystems in most researches, thus leading to little practicability to water allocation practice. Therefore, this paper advanced an idea based on the calculation of EWR on a proper ecosystem status determined by the demand of a region or a watershed for eco-environmental functions and services. Zhifanggou watershed, which is located in Ansai county on the Loess Plateau and suffering from serious water and soil loss, was chosen as the study area. Based on the existent study of the relationship between soil erosion and land use structure, the land use structure of Zhifanggou watershed was determined according to the objective of water and soil conservation, and then the EWR of Zhifanggou watershed was calculated according to the determined land use structure. EWRs corresponding to different scenarios of land use structure and different objectives of water and soil conservation were compared and discussed. The result shows that the proper objective of water and soil conservation for Zhifanggou Watershed is 1000 t/(km²·a) of soil loss tolerance, and the corresponding EWR is 1.77×10⁶m³, which occupies 39.0% of the total annual precipitation. By the comparison between the calculation result based on the status quo of ecosystems and that of ours, our idea was proved more practical.