Abstract: Based on the simulated topographic parameters including slope, azimuth and screening angle and observed global radiation on flat-plate, a numerical model to calculate the long-term average of global radiaton over rugged areas is developed. This paper consists of the development of the model, the numerical tests for selection the model parameters and discussion to the modeled results in the part of Dabie Mountain. It is manifested that the influence of terrain on global radiation is quite remarkable. In principle, the model is suitable for simulation the global radiation in any mountain with different scales.