Abstract: In order to solve the bearing capacity calculation problem of the steel reinforced concrete composite beam in steel support system of foundation excavation, based on the plastic design theory and several assumptions, the calculation formulas for the bending capacity of the steel-concrete composite beam under axial force were derived,which had universal applicability, and the calculated results were in good agreement with the test results, indicating that the calculation formulas given in the paper were reliable. The formulas were summarized and unified, it was found that when axis forces changed,M_u -δ (the distance between the axial force action point and plastic neutral axis) curve ws composed of one or more quadratic parabolas, and the parabolas opened downward. The smaller δ, the larger M_u. When δ was equal to zero, the bending capacity reached the largest, and the corresponding axial force calculation formulas were given. The curvatured of the M_u-N curve was mainly determined by the width and strength of composite beam. The greater the material strength and width, the smaller the curvature, the flatter the curve.