The arid and semi-arid areas generally face the degradation of natural resources, poor vegetation conditions, and serious soil erosion. In this paper, a spatio-temporal assessment model for the rainwater resources utilization and its driving forces is studied and constructed, and a typical watershed is selected for application and verification. The model is based on SWAT (Soil & Water Assessment Tool) and GTWR (Geographically Temporal Weighted Regression) for secondary development. Two indicators are proposed to characterize the utilization of rainwater: rainwater resources utilization quantity (RRU) and rainwater resources utilization rate (RRUR). To further verify the performance of the model, the scenarios of different watershed management measures were simulated and evaluated. The results show that the model can accurately evaluate the RRU, RRUR, and driving force. The annual average value of the RRUR in the typical watershed is 0.44, and the utilization rate of the middle reaches is higher than that of the upper and lower reaches. Meanwhile, the model can evaluate the RRUR and driving force of different land management scenarios. The driving effects of meteorological, topographical, vegetation, and other factors on the regional RRUR exhibits certain spatiotemporal differences, among which the leaf area index (LAI) is the key driving factor. The framework can provide scientific guidance for improving the rainwater resources utilization rate (RRUR) and alleviating ecological problems.