Abstract: The simulation of soil moisture on the Qinghai–Tibet Plateau is influenced by the spring snowmelt process, which involves considerable uncertainty and substantially influences summer climate simulations. To explore the effects of snowmelt-induced variations in spring soil moisture on summer climate modeling, this study incorporated a relaxation term representing the snowmelt process into the Pleim–Xiu assimilation soil moisture scheme within the WRF (Weather Research and Forecasting model). Cross-season climate simulations were conducted to evaluate the effect of spring snowmelt on soil moisture and surface nonadiabatic heating over the Tibetan Plateau. The study also analyzed how snowmelt-driven soil moisture anomalies in spring influence summer climate patterns across China. The results show that including the snowmelt process in the land surface model’s assimilation system brings simulated soil moisture values closer to observations, though notable spatial variations remain. The improved assimilation scheme reduces errors related to soils moisture in the plateau, with especially notable improvements in the southern plateau. Low deviations in soil moisture enhance the accuracy of simulated surface latent heat, though improvements in surface sensible heat simulation are limited. Moreover, incorporating the snowmelt process into the assimilation system improves the model’s accuracy in simulating summer precipitation in northern China and reduces the overestimation of summer temperatures in eastern China.