Abstract: The Source Region of the Yellow River (SRYR) is the main runoff-producing area and an important water conservation area of the Yellow River Basin. It is scientifically important to understand and explore the land–surface process and regional water cycle characteristics and reveal the impact of land–hydrological coupling processes over the SRYR. Based on the China Meteorological Forcing Dataset (CMFD), Climate Prediction Center (CPC) Morphing Technique (CMORPH), Tropical Rainfall Measuring Mission (TRMM), and Global Land Data Assimilation System (GLDAS) precipitation from 2009 to 2018, the precipitation accuracy of four types of precipitation products is evaluated in this research. Driven by the optimal precipitation product, the standalone Weather Research and Forecasting Hydrological (WRF-Hydro) modeling system is chosen to explore its applicability in streamflow simulation over the SRYR. The results indicate that the four types of precipitation products can reflect the distribution characteristics of precipitation, while differences in quantity and detail are substantial. CMFD products perform better in capturing the evolution characteristics of precipitation at different spatial and temporal scales. The correlation coefficient between CMFD products and gauge observation is 0.99, and the root mean square error is 0.25 mm. In the ability to indicate precipitation, the overall performance of the four types of precipitation products presents that CMFD>CMORPH>TRMM>GLDAS and the average critical success index of CMFD is more than 0.93. The WRF-Hydro model calibrated by the sensitivity parameters performs well in simulating monthly streamflow over the SRYR. The Nash-Sutcliffe efficiency coefficient (NSE) is above 0.92 during the calibration period, while the simulation results are significantly better in the high flow years than in the low flow years, with a NSE of 0.15 during the validation period, which is related to the nonlinearity of precipitation and streamflow. This research scheme and results have the potential to provide references for a large-scale watershed hydrological simulation and projection in the semiarid region of the subcold zone.