Abstract: Based on the derived general expression for the displacement of a point in a surrounding rock mass caused by excavating under the action of self-weight volume forces from similarity theory,by means of dimensional analysis,and comparing with the results of the numeral simulations,an empirical formula of parametric ratios expressed in geometric,physical and mechanical parameters is proposed,which shows the quantitative relationships between the displacement of a point in a surrounding rock mass caused by excavating in a linearly elastic semi-infinite body and any one of the parameters,including the specific weight of a rock material,the modulus of elasticity for the material,the size of a cross section of a tunnel and the distance from the earth surface to the center of the cross section. And the conditions under which the formula holds and its applications are discussed, and the methods for use it are given. A main conclusion says that,in the case that the geometric similarity law is not completely satisfied,under the given other conditions the displacement of a point in the rock mass surrounding a tunnel is proportional to the product of the distance from the center of cross section to the earth surface and the size of the cross section and is independent of the shape of the cross section.