Aiming at the rebound deformation of soil at the bottom of foundation pits caused by excavation unloading, the characteristics of soil elastic modulus changing with the unloading stress path during excavation was first considered, then the calculation formula of soil deformation modulus under unloading stress path was derived. Considering the change of stress at the excavation surface of foundation pit below the ground surface, based on the Mindlin stress solution, the additional stress of soil at the bottom of rectangular foundation pit caused by excavation unloading was calculated. The rebound deformation of the soil at the bottom of foundation pit caused by excavation was calculated by the layer-wise summation method. Combined with some engineering examples in the existing literature, the heave deformation of pit bottom caused by excavation was calculated by this calculation method, then the calculation results were compared with the actual monitoring data. The results showed that the proposed method can effectively predict the heave deformation of pit bottom caused by excavation, thus it can be used as an effective prediction method in this field.