Under global warming, China is more vulnerable to the threat of extreme climate events. Studying the future climate change in China and providing more accurate future projections are of great significance for disaster prevention and mitigation, as well as policy-making in response to climate change. Based on the simulations of the global climate models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6), we adopt a weighted scheme of Climate Model Weighting by Independence and Performance (ClimWIP) to carry out the multi-model ensemble constrain of mean and extreme temperature and precipitation over China region. Based on the performance evaluations of the constrained ensembles, the projected changes at the 1.5 and 2 ℃ global warming under the SSP5-8.5 scenario are studied. Results show that the ClimWIP scheme has better performance when compared to the unweighted scheme, which reduce the climatology bias of ensemble. The spatial correlation coefficient between temperature indices and observations exceeds 0.98, and standard deviation ratios are close to 1. The spatial correlation coefficient between total precipitation (PRCPTOT) and heavy precipitation (R95P) with observations exceeds 0.92 and standard deviation ratios between 0.8 and 1.0. The regions with higher projection uncertainty are mainly in Northern China and Tibetan Plateau for the temperature indices, and in North China and Northwest China for the precipitation indices. The projection uncertainty by the ClimWIP scheme is reduced when compared with the unweighted scheme. The reduction is greater for temperature indices in Southern China and Tibetan Plateau, while precipitation indices show a significant decreased in uncertainty in Northeast China and northwest Xinjiang. Under 2 ℃ global warming, the uncertainty of annual mean temperature (Tas), maximum temperature (TXx), and minimum temperature (TNn) in China is reduced by 19.2％, 22.1％, and 17.8％, respectively, while PRCPTOT and R95P is reduced 3.3％ and 4.7％, respectively. Regarding to the geographic distribution, ClimWIP scheme would see larger warming in Northern China and Tibetan Plateau for the temperature indices. More intense precipitation concentrate in Northwest China and Tibetan Plateau. Under an additional 0.5 ℃ global warming, the temperature response in China region is stronger than that of global response, with an average higher warming about 0.2 ℃. The response of TNn in parts of Northeast China even more than three times additional warming. And there would be an additional increase about 5.2％ and 10.5％ for PRCPTOT and R95P, respectively. From the perspective of probability projection, at the 2 ℃ global warming, the warming magnitude in most regions of China would be likely larger than 1.5 ℃ compared to the current climate state (probability value>50％), and the probability in parts of Northern China and Tibetan Plateau would be much higher (probability value>90％). For the precipitation indices, the probability of wetter condition in Northwest China and North China would be larger, with a likely response magnitude exceeding 10％, 25％ and -5 days for PRCPTOT and R95P and continuous dry days (CDD) (probability value>50％). The ClimWIP scheme can reduce the uncertainty of future projections and provide more accurate future projections, and more model evaluation metrics such as trends and key physical processes can be considered in ClimWIP scheme in the future. Alternatively, multi-modal large ensembles and high resolution models can be used to improve the reliability of future projections.