Abstract: We evaluate the ability of models to simulate the aridity index (AI) and project the dry/wet climate changes in China under ther epresentative concentration pathway (RCP) 4.5 scenario using experimental data of a high-resolution regional climate model (RegCM4) nested within three global climate models. For the reference period of 1986–2005, RegCM4 can reasonably simulate the spatial pattern of AI in China, and the results of the simulated AI slightly differ between the two methods for calculating potential evapotranspiration, especially in the western high-altitude and northern regions over the country. Based on the projections of RegCM4, the AI averaged over China would decrease by 2%–4% and 2%–5% in the middle (2046–2065) and end (2081–2098) of the 21st century relative to the reference period, respectively, with central Northwest China becoming wetter and other regions becoming drier. The predominant factor influencing the future dry/wet climate changes in China varies with regions. Precipitation is the leading factor in central Northwest China, while in the other regions, temperature increase plays the dominant role via potential evapotranspiration changes.