Water resource conservation can be calculated with soil porosity, a water balance method, base flow estimation, and a depletion curve method. However, most of these belong to static state calculations in a single period. This study used the Stormwater Management Model (SWMM). The SWMM can dynamically simulate the water resource conservation capability with land-use changes, and determine the impacts of land-use changes in the study area. The research area of the Deji Reservoir was the upstream portion of the Dajia River. Meteorological, hydrological, and landuse data were gathered, and 4 yr of land-use changes were put in the SWMM model to analyze the Deji Reservoir water resource conservation. Furthermore, impacts of land-use changes on water resources conservation changes were also estimated. Results showed that when the proportion of forest land use was higher, the resource conservation capacity was higher. About 61% of the annual rainfall was conserved in the watershed of the Deji Reservoir. Water resource conservation can be more finely calculated in the future, for example, using different kinds of trees. In addition, water resource conservation is affected by various factors, such as rainfall, the rainfall intensity, geology, slope, etc. This study used rainfall data from 2009 and 2010 to analyze water resource conservation. Results showed that the impacts of different rainfall patterns on water resource conservation were greater than those of land-use changes. Under the same rainfall pattern, different land uses also had an obvious influence on the amount of nutrients.