Most basins in the semi-arid region of the Loess Plateau lack gauged data on precipitation and runoff. The degree of water resources security seriously restricts the rapid development of the social economy. To determine the available amounts of rainwater/stormwater resources and the utilization potential in the ungauged basin, this study took Si Jiagou Basin as an example, established a SWAT model based on the gauged basin, analyzed and calculated the model output after calculating, it is found that the total rainwater/stormwater resources in the basin in 30 years was 602.68×104m3, with a considerable utilization potential. The rainy season is the crucial period of rainwater/stormwater resource collection, and the proportion of available utilization is 93.52%. The profit of 2-10mm accounts for 53.81% of the total in the rainy season, which is the water-saving potential area. The resources of 1-2mm account for 15.65% of the total in the rainy season, which is the main point and direction of the utilization level. The higher the precipitation guarantee rate, the more significant the proportion of rainwater/stormwater resources in the non-rainy season. The results can provide essential data and theoretical basis for the construction of facilities for the efficient use of rainwater/stormwater resources in the semi-arid region of the Loess Plateau.