Abstract: Impacts of greenhouse ef fects (2×CO2)on climate change over China as simulated by a regional climate model have been investigated. The model was based on RegCM2 and is nested in one-way mode within a global coupled atmosphere-ocean model(CSIRO R21L9 AOGCM).Two multi-year simulations, the control run with normal CO2 concentration and sensitive run with doubled Cq concentration are conducted. As Part I of the publications, results of control run of the CSIRO, i.e. its simulations of present climate in China,are analyzed briefly. It shows that the model has a certain ability in the simulations of surface air temperature and precipitation over China. Therefore, its results can be used as initial and boundary conditions to drive the regional model. Analysis of control run of RegCM2 shows that with a high resolution, the model improves the simulations of surface air temperature and precipitation in China compared to the CSIRO model, especially for the precipitation. The spatial correlation coefficient between simulated and observed annual temperature increased from 0.83 in the CSIRO to 0.92 in the RegCM2 and for annual precipitation from 0.48 in the CSIRO to 0.65 in the RegCM2.A similar improvement in the RegCM2 compared to the CSIRO was found in all simulated months. The main improvement for surface temperature is that RegCM2 can simulate the fine scale structure of temperature caused by topography. RegCM2 greatly improved the spatial distribution of precipitation by eliminating the virtual precipitation center in mid-west China, which was simulated by many other GCMs. The precipitation simulated by RegCM2 in north and northwest part of China is smaller than that by CSIRO which makes it closer to the observation. It suggests that with the good performances of climate simulations, RegCM2 can be widely used in the regional climate study of China, e.g. climate change scenario simulations.