Abstract: In the process of rock cooling and long geological evolution, some stress are enclosed. The phenomenon of enclosed stress in rock is gradually recognized. In order to reveal the existence form of locked-in stress in rock, the quantity of locked-in stress is measured and calculated by the tilt solid ψ method with an X-ray diffractometer, and the principal of locked-in stress is determined. The results show that the quartz particle size is about 40μm in the target area of quartz vein slate samples. In the diffraction angle range of 152°~156°, the diffraction peak of (324) crystal plane obtained with different ψ is consistent, which proves the existence of sealing stress. The sealing stress of quartz vein measurement point is compressive stress. The maximum principal stress (22.71 MPa) is parallel to the vein body strike , and the minimum principal stress (12.97 MPa) is vertical to the vein body strike. The linear correlation law of 2θ–sin²ψ was not found in the matrix measurement points. The measurement method of confining stress proposed in this paper can provide reference for subsequent observations and related research of confining stress of different types of rocks.