Abstract: The silvopastoral system boundary was studied using moving split-window approach in Robinia pseudoacacia forests and grassland system in the loess region of western Shanxi Province，northern China，and the characteristics of herbaceous plant diversity were analyzed by the method of α diversity and β diversity. The results showed that：1) the boundary of R. pseudoacacia forests and grassland system could be discriminated clearly when the window width reached 8，and the influencing range of the silvopastoral system was 8 m，i.e.,from 4 m inside forestland to 4 m inside grassland，which was consistent with the result of hierarchical cluster for similarity index (SI) of quadrats; 2) α diversity analysis showed that the species diversity in grassland was the highest，and there was the largest unevenness in the boundary of silvopastoral system; 3)β diversity analysis showed that the changes for forestland plant species were dramatic，indicating that the differentiation of woodland habitats was bigger and the rates of species being replaced were higher in forestland than in grassland.