By short introduction of field test for specimens of spreading foundation on rock sub-grade and on the basis of field test data for specimens of spreading foundation on rock sub-grade,the distribution curves of sub-grade reaction at each level of the load are plotted and the rule of the curves for each type of specimen is summarized.By comparison of the results measured in other foundation soils,the major reasons for differences among the different foundation soils in the distribution of sub-grade reaction and the factors which influence the distribution of sub-grade reaction are presented:the differences in character of the sub-grade and the load.It can provide some reference for calculation of key section's internal force and research and practical application in foundation engineering on rock sub-grade.