Abstract: A photosynthetic active radiation（PAR） model of actual terrain was established based on the distributed models of direct and diffuse radiation over mountainous terrains, in which the digital elevation model data and all the factors relating to topographical factors were combined effectively. According to the model, the spatial distribution of PAR in average month, season and year under temperature ≥0℃ and ≥10℃ were evaluated in Shaanxi province. The effect of various local topographic factors on PAR was also discussed. The results showed that the PAR distributed model was reliable. Spatial distribution of PAR with temperature ≥0℃ and ≥10℃ indicated that there were abundant solar energy resources in Shaanxi province and the agricultural production would improve in theory. The Effect of topographic factors on PAR over mountainous terrain were obviously, the PAR amount reduced gradually with the slope increasing, larger in southern direction and smaller in northern direction, distributed symmetrical in east and west slope. Moreover the effect of local topographic factors on PAR changed with season going. The topographical effect was more obviously in winter than in summer, because of lower sun elevation angle.

Key words: Photosynthetic active radiation, Local topographic effect, Different temperature range, PAR in Jan. (PAR1), PAR in July (PAR7), Slop, Aspect