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A regional climate model is employed to simulate the aerosols (dust, sulfate, black carbon, and organic carbon) and their direct effect on the climate over China. The emphasis is on the direct radiative forcing due to the change in mixing state of aerosols. The results show that direct radiative forcing is significantly different between externally and internally mixed aerosols. At the top of the atmosphere (TOA), the radiative forcing of externally mixed aerosols is larger than that of internally mixed ones, especially in the Tarim desert region where the difference is about 0.7 W m(-2). At the surface, however, the situation becomes opposite, especially in the Sichuan basin where the difference is about -1.4 W m(-2). Nonetheless, either externally or internally mixed aerosols in China can result in a significant cooling effect, except for the warming in South China in winter and the slight warming in North China in February. The cooling effect induced by externally mixed aerosols is weaker than that induced by internally mixed aerosols, and this is more obvious in spring and winter than in summer and autumn. In spring and summer, the inhibiting effect of externally mixed aerosols on precipitation is less than that of internally mixed aerosols, whereas in autumn and winter the difference is not obvious.