Abstract: Based on CAS-ESM2.0 (the second-generation Chinese Academy of Sciences Earth System Model), this study first introduced a PHS (plant hydraulics scheme) into the land surface component model, CoLM (Common Land Model), to replace the original empirical scheme. Subsequently, two sets of 34-year (1981–2014) Atmospheric Model Intercomparison Project numerical simulation experiments were performed to investigate the impacts of the improved PHS on the simulation of summer precipitation over China. The results demonstrated that the improved PHS significantly reduced the climatological biases in the CAS-ESM2.0 model in summer precipitation simulation. Notably, the updated scheme reduced the underestimation of precipitation in eastern China and the Tibetan Plateau, as well as the overestimation of precipitation in the western Sichuan region. Additionally, the scheme enhanced the simulation of interannual variability of summer precipitation and the frequency of extreme heavy rainfall days. Further analysis revealed that the improved PHS substantially reduced model biases in soil moisture, specifically the overly dry bias over the Yangtze River basin and the wet bias over the Tibetan Plateau. The modifications also reduced biases in the simulation of surface sensible heat flux and surface latent heat flux over the Yangtze River basin, North China, and Tibetan Plateau, thereby improving the model’s representation of land–atmosphere interactions. The improved land–atmosphere coupling significantly enhanced the model’s ability to simulate the East Asian monsoon circulation. Specifically, the improved model demonstrated a reduction in negative bias when simulating sea-level pressure over the northwestern Pacific, which favored the intensification of the southwest monsoon and enhanced moisture transport from the northwestern Pacific to eastern China. Concurrently, an anticyclonic circulation anomaly was detected in the lower troposphere, which effectively mitigated model biases in the underestimation of weak southerly winds and insufficient moisture convergence over eastern China, resulting in a remarkable reduction of precipitation underestimation in eastern China. These findings underscore the importance of accurately representing land–atmosphere interactions, particularly by incorporating plant hydraulic processes, for improving simulations of East Asian summer precipitation.