Abstract: Solar radiation is the most important energy in surface physical，biological，chemical process，and is also the basic input parameter in the climatology，hydrology，atmospheric science and climate change. Different slope and aspect accept different amount of solar radiation in the mountain area，however，the ground observation points in mountain area are small，limited and uneven，continuous distribution of solar radiation values could not be got through interpolating or extrapolating，so it is necessary to establish a reasonable distribution of solar radiation and accurately simulate the solar radiation in the surface. Based on Arcgis，Envi and C++，this paper propose an estimation model of solar radiation in mountainous area under sunny condition. Using as a source of reference on the domestic and foreign research results of solar radiation，based on the full consideration of the topographic parameters such as elevation，slope，aspect，shadowing factor，the sky visible factor，using the Modtran atmospheric radiative transfer model to calculate the atmospheric transmittance with atmospheric data (with the terrain changes)，MODIS product is used to calculate albedo，establishing a more reasonable and feasible model to calculate solar radiation in mountainous area. With the test area at mountainous area on the upper reaches of Heihe River，Gansu Province，China，the paper used the model to simulate the direct solar radiation，scattered radiation，reflected radiation and total radiation in the surrounding terrain，analyzed of slope，elevation，the spatial distribution of solar radiation，and applied the measured results to validate the model. The results showed that with the height is increasing，the total solar radiation is increasing，too，but the scattered radiation is decreasing. The surrounding terrain reflected radiation shows a general increasing trend，but the rate of the total radiation is more and more slow. Because with the increase of altitude，atmospheric is thinner，water vapor content is less and temperature is lower，solar radiation is increasing. With the increasing of the slope，the total amount of radiation increases firstly and then decrease; slope and solar altitude is different，the solar incident angle is different，too. Only when sunray and the normal of slope are parallel，solar radiation will reach the maximum，slope will be the height of the sun angle at the same time. The maximum radiation value appears in the East. The mean values of maximum radiation is in the southeast aspect，average minimum radiation appears in west aspect，radiation in sunny slope is larger than that in shade，because the sun is at the southeast aspect on the computation time，larger values of solar radiation will appear in consistent with the location of the sun，the west relative to the southeast，accepts solar radiation at the latest，the radiation is the least. The results show that the model can reflect the spatial distribution of the total solar radiation in mountainous area. The model could be a reference on estimating solar radiation over rugged terrains.

Key words: digital elevation model（DEM）, MODIS, modtran, mountainous solar radiation