Abstract：The concept of tectonic stress plane (TSP) is defined as an ideal curved plane drawn by the locations with different depths where the influence of non-tectonic stress disappears. Therefore，to U-like valleys，three-dimensional model with consideration of different factors，such as valley width，mountain slope，mountain height，gravity loading，and horizontal lateral compression，respectively，is made to conduct 3D finite element modeling research on the spatial variation law of the maximum horizontal principal compressive stress in crust. By mathematical statistics and analysis，the empirical formula is given to show the TSP depth changed with the above factors. The research shows that horizontal lateral compression and mountain height are the major factors to affect the TSP depth，and that when the ratio of the gradient of horizontal lateral compression varied with depth to the gravity gradient is obtained as one，the TSP depth is approxinatelly equal to mountain height.
