Abstract: In the initial support of soft rock tunnels, the combined support of steel frame and locking foot anchor pipe is an effective and economical support measure to control the deformation of surrounding rock of the tunnels. Among them, the setting angle of the locking foot anchor pipe is an important parameter affecting its support effects. Based on the existing mechanical analytical model for steel frame + locking foot anchor pipe after excavation of the upper bench, the mechanical analytical model for steel frame + locking foot anchor pipe after excavation of upper and middle benches is derived by using the method of structural mechanics, so as to obtain the theoretical formula for the setting angle of the locking foot anchor pipe and the settlement of the steel frame vault after excavation of the upper and middle benches. At the same time, based on the measurement analysis of the vertical pressure of the surrounding rock, the relationship between the angle of the locking anchor pipe after the excavation of the upper and middle steps and the settlement of the steel frame vault is obtained, and the Zhonghe Tunnel is used as the engineering basis to determine the optimal angle of the locking anchor pipe after the excavation of the upper and middle steps. The results show that the settlement of the tunnel vault obtained by the established mechanical model for steel frame + lock foot anchor pipe after excavation of upper and middle steps is basically consistent with the measured value. According to the theoretical formula settlement of steel arch, the optimal setting angle of locking foot anchor pipe of step in the tunnel is 60 ° ~ 70 °. The research results can provide a theoretical basis for the optimization design of the dip angle of the locking foot anchor pipe in the step excavation of deeply buried tunnels.