Abstract: Spring snowmelt is a critical source of soil water recharge in high-latitude regions, but these recharge processes have become increasingly uncertain under climate change. Accordingly, this study focuses on the black soil region of Northeast China and integrates the SWAT model with CMIP6 climate projections to simulate hydrological processes under four future climate scenarios (SSP126, SSP245, SSP370, and SSP585). A PLS-SEM approach is applied to quantitatively assess the mechanisms through which spring snowmelt influences soil moisture. The results show that the following: ① Spring snowmelt decreases by 0—30 mm across the four scenarios. ② Across the four scenarios, soil moisture decreases by 5%, 7%, 12%, and 12%, respectively, as emission levels increase in the 2061—2100 timeframe. Significant spatial heterogeneity is observed—high-elevation mountainous areas experience pronounced reductions, whereas parts of the Northeast Plain exhibit increases in soil moisture because enhanced rainfall offsets the negative impacts of reduced snowmelt. ③ In the baseline period, the direct path coefficient snowmelt exerts on soil moisture (0.396) exceeds that of rainfall (0.247). Under future scenarios, the direct effect of snowmelt on soil moisture weakens by 24%, while that of rainfall strengthens by 42%, making rainfall the dominant factor. This study provides scientific support for adaptive water resource management in cold regions.