For identifying the effects of spatial distribution of rainfall erosivity on soil loss, Zichang catchment of Chinese loess hilly-gully area was taken as an example, and the concept of regional gravity center was used to analyze the spatial distribution of rainfall erosivity. The effect of the spatial movement of rainfall erosivity gravity center on soil loss in different years was analyzed based on GIS tools. The results indicated that the distance between gravity centers of rainfall erosivity and hydrological station and that between gravity centers of rainfall erosivity and gravity centers of steep slope grade (higher than 15°) had significant influence on soil loss. When gravity center of rainfall erosivity was in the middle place between hydrological station and gravity centers of steep slope grade (higher than 15°), there would also be more soil loss. The changes of gravity centres of rainfall erosivity from north to south had little effect on soil loss. However, the changes from west to east had much effect. For catchment, with the changes of spatial distribution of rainfall erosivity, the fitting relations between rainfall erosivity and slope grade, and land use, and hydrological station would be changed, which would lead to the amount of soil loss increased or decreased.