Abstract: Author presents stress component's expression under polar coordinate while a single force is applied to horizontal rock formation by means of Airy's stress function.Author regards topography's effect on underlying horizon rock formation as distributed load,thus obtains expression of subsidiary stress induced by distributed load by integral action.According to present achievement,when subsidiary stress caused by distributed load is less than 20 percent of static lateral pressure induced by gravitation,distributed load's effect may be ignored. Therefore,the expression of topograpthy influence depth on self-weight stress field is obtained.Furthermore,the paper illustrates how to obtain topography influence depth on self-weight stress field of horizontal,homogeneous and isotropic strata.