Abstract: Based on the analyses of meteorological deta in 1961—1980 and distribution of 18 representa-tive species of arborn and shrubs in shelter-forest districts of“San Bei”(northwest,north andnortheast of China),it's concluded that(1)heat condition in these districts can meet theneeds of most tree species and find itself in an optimum range needed for tree's normal grow-th;(2)water condition is the limiting factor for the distribution of tree'species in thesedistricts;(3)minimum value of coldness index must be considered when tree species are in-troduced northward

Key words: Soil moisture, Shading levels, Photosynthetic characteristics