Abstract: The paper puts forward some questions to the application of the formula: D=P/d, where D, P and d represent depth,pressure and specific density, respectively. This formula stems from a fluid mechanical principle, the Pascal's principle, describing the relationship between pressure and depth in static fluid. This formula is applied to fluid material only. If the material is a solid, and it may undergo shear or differential stress, then this formula can not be applied. All rocks existing from the Earth surface down to the boundary between the mantle and the core show solid character. When a foece is acted on a solid unit, no matter the force is tectonic or gravity, there always exist two stress parts in the solid stress field: the uniform stress and the differential stress.However, in the case of liquid material, the stress is uniform, but not differential. The results of geo-stress measurements show that the horizontal stress acted on the vertical section should be greater than the vertical stress acted on the horizontal section;and that the nearer the distance to the orogen belt or shear zone, the greater the horizontal stress is, thus indicating the leading role of tectonic force in the crust stress field. In fact, the force pushing the plate movement is mainly the horizontal stress, but not vertical stress. The total static pressure at a position in crust is composed of at least two parts: the pressure induced by the tectonic activities and the pressure induced by the gravity. The former pressure is the additional tectonically-induced static pressure. The reasonable method to calculate the depth should be the subtraction of the additional tectonically-induced pressure from the total pressure, and then divided by the rock specific density, i.e. D = (P-Pt)/d, where Pt represents the additional tectonically-induced static pressure.