An experimental study of the confining pressure, i.e. additional hydrostatic pressure initiated by the tectonic force is presented. The experimental progress is that the σ 1 is gradually increasing from 0 in a limiting movement ( ε 1=0) in the σ 1 direction and the speed rate of the accelerating load is 0.4 MPa·s -1 in the lateral and level directions. When σ 2= σ 3<200 MPa, Δ σ l is nearly lacking, Δ σ l is increasing at a high speed only when the horizontal force reaches 250-380 MPa, and Δ σ l almost ceases to increase at the level force of 380 MPa. It is calculated that the tectonic force can produce the confining pressure which is gradually increasing with σ 2= σ 3 before it reaches 380 MPa in an experiment. It is supposed that the horizontal force is almost all transformed into the confining pressure with the increase of the creep deformation of rocks. An experimental study of the confining pressure, ie, additional hydrostatic pressure initiated by the tectonic force is presented. The experimental progress is that the σ 1 is gradually increasing from 0 in a limiting movement (ε 1 = 0) in the σ 1 direction and the When σ 2 = σ 3 <200 MPa, Δ σ l is nearly lacking, Δ σ l is increasing at a high speed only when the horizontal force reaches 250-380 MPa, and Δσ l almost ceases to increase at the level force of 380 MPa. It is calculated that the tectonic force can produce the confining pressure which is gradually increasing with σ 2 = σ 3 before it reaches 380 MPa in an experiment. It is that that horizontal force is almost all transformed into the confining pressure with the increase of the creep deformation of rocks.