Solar radiation is the ultimate energy source for ecosystems and the base for all ecological processes. The radiation in the relief area will be obviously affected by the terrain. SUNLIGHT model takes such topographic effect into account in detail and can be used to calculate the solar radiation including direct, diffusive and reflective radiation of each point within a watershed scale. The model first calculates the topographic parameters such as slope, azimuth, view factor and sheltering angle of each point in a watershed based on DEM, then decides the sun rising and sun setting time angles of each point by comparing the angles calcualted from sun orbital equations for any slope and aspect and the sheltering angle in the sun rising and sun setting direction. The direct solar radiation can be calculated after getting the actual sun rising and setting angles of each point. The diffusive and reflective radiation can be simply calculated by using topobraphic parameters and actual survey data of a flat area site without topographic effect.Da’an paleochannel region is a newly found paleochannel in the Songnen Plain. It is the current most promising barren area that can be reclaimed. The paper applies the SUNLIGHT model in this region to know the detail spatial distribution of solar radiation. The results show that the possible direct radiation on May 15, 1994 was about 8.483 MG/m² with normal deviation of 2.041 MJ/m². Though the radiation distributes more evenly than in other relief area, it will be changed sharply in the slope area. The regression function between the direct solar radiation and topographic parameters can be represented as:
S_dr = 0.002H-3.435α + 0.029β + 20.498VF-11.71
(R-0.41)
where H,α, β and VF represent altitude, slope, azimuth and view factor respectively. And PCA analysis shows the most important topographic factors that affect direct solar radiation in this area are view factor and slope. Their correlative coefficients with the first axis are 0.332 and-0.29 respectively. The results of the model have indicted that it can give a precise calculation for the distribution of solar radiation and thus provide the background for further study.