Abstract: Taking an auxiliary shaft project under deep thick alluvial layer as the research object, the process of shaft excavation is simulated by using finite difference software FLAC^3D, and the variation rules of vertical and radial strain and deflection of shaft wall at different depths are monitored by using optical fiber monitoring method. The results show that: the displacement changes show a nonlinear increasing trend with the increase of shaft excavation depth; the horizontal radial displacement is affected by the lateral pressure of the cylinder wall, and the displacement tends to increase; the monitoring results of shaft wall strain are mainly influenced by the change of shaft wall temperature, and the tensile strain and compressive strain alternate back and forth. The maximum deviation value of the shaft in the later period of monitoring is 0.029 m, and all the monitored values are within the allowable range of safety, so the shaft wall structure remains safe and stable.