Abstract: 目的To improve the reliability of future summer precipitation projections over eastern China, 资料this study uses outcomes of climate model from Phase 6 of the Coupled Model Intercomparison Project (CMIP6) and 4 initial-condition large ensemble simulations. 方法Through the perfect model test framework, the constraint variables and their spatial scales in the Climate Model Weighting by Independence and Performance (ClimWIP) scheme are optimized. 结果 结论Results indicate that using the historical global-scale mean temperature trend as a constraint significantly improves projection reliability compared to using smaller-scale constraints. Moreover, the ClimWIP scheme, which considering both historical global temperature trend and regional precipitation mean state, provides the most reliable projections. The optimal projection indicates that summer total precipitation in eastern China will increase by 6.8% (2041—2060, mid-21st century) and 12.9% (2081—2099, end-21st century), relative to the 1995-2014 baseline, under the SSP5-8.5 scenario. More notably, summer extreme precipitation exhibits stronger responses, increasing by 16.9% and 28.7% during the corresponding periods. Northern China shows even more pronounced changes by the end-21century, with summer total and extreme precipitation increasing up to 19.1% and 35.5%, respectively. Compared to the multi-model ensemble mean (MME), the optimal projection scheme enhances the interannual variability of summer precipitation, indicating that future fluctuations between droughts and floods will become more pronounced. It also reduces the uncertainties of future projections for summer total and extreme precipitation, primarily for the upper bound. The largest uncertainty reduction occurs in Northeastern China (about 40%) by the mid-21st century, while in Northern China and the Yangtze River Basin (about 50%) by the end-21st century.