Based on the KS tunnel project of the second phase of water supply project in North Xinjiang, through the real-time monitoring of the internal and external flange stress of the steel arch frame and the analysis of its distribution characteristics and change rules, the axial force and bending moment of the steel arch frame are calculated by the principle of mechanics of materials, and the safety level is analyzed by combining the stability judgment process of the steel arch frame. Researches have shown that: The overall performance of the steel arch is in compression state, and the internal stress at the same measuring point is generally greater than the external stress. The maximum stress of the steel arch is 50.88 MPa, which is located at the side wall. The axial forces of the steel arch are all negative value, showing the compression state, the maximum value is -94.25 kN, which is located at the side wall. The bending moment of steel arch gradually changes from negative value to positive value from top to bottom, the maximum value is 3.22 kN. m which is located at the arch shoulder. After stabilization, the bending moment is negative except for the side wall. According to the stability of the steel arch frame, the stability grade of the arch crown is safety, and the basic safety is the arch shoulder, the arch waist and the side wall. During the construction, the observation should be strengthened to reduce the occurrence of safety accidents.