Water is a basic natural resource that all living creatures need to survive and cannot be replaced. Ecological water demand plays an extremely important role in maintaining the balance beween the ecosystem and the sustainability of the biocapacity of river basins, especially arid inland basins. In this study, the basin-and county-scale Shule River Basin Landsat TM/ETM+/OLI remote sensing data (30 m resolution) were used to interpret the Shule River Basin (SRB) land use data for the past 20 years. The analysis was based on the five phases of land use data, multi-year hydrology and water resources basic data, and SRB field surveys and observations, The multi-year hydrology and water resources basic data for the basin and the field surveys and observations results were used to calculate the ecological water demand of the SRB over the past 20 years. The spatial-temporal evolution of ecological water demand and biocapacity in the SRB were also investigated. Over the past 20 years, the total biocapacity of the SRB showed an increasing trend. The ecological water demand of the natural vegetation in the basin also increased significantly. A statistical analysis of watershed biocapacity and ecological water demand showed that biocapacity and overall ecological water demand had increased over the past 20 years. Furthermore, there was also a significant positive correlation between watershed biocapacity and the ecological water demand (0.6076). At the county scale, the correlation between the ecological water demand and biocapacity was significantly positive. In particular, the positive correlations between ecological water demand and the biocapacities of forest and grassland were the strongest, and the goodness of fit (R²) reached 0.8519 and 0.7235, respectively, which indicated that the ability to explain forest and grassland ecological water demand changes was stronger when there were changes in the biocapacity of forest and grassland and the coupling relationship between the two was closer. Based on spatial hotspot analysis, the hot and cold regions of biocapacity and ecological water demand show similar spatial pattern, which indicates a positive correlation between them on the spatial scale. Furthermore, if the future trend in biocapacity is constrained, the ecological water demand can be optimized and controlled, and the utilization of water resources will improve.