Deformation of the surrounding strata is inevitably induced by foundation pit excavation, which in turn affects the safety of nearby buildings. In this study, a calculation method for analyzing the deformation of surrounding strata induced by foundation pit excavation is proposed. The occurrence and evolution of strata deformation are regarded as three independent processes, and the deformation is decomposed into three components: ground loss, wall friction, and excavation unloading. Based on stochastic medium theory and the Mindlin solution, the three-dimensional strata deformation induced by each component is derived separately. Under the small-deformation assumption, a three-dimensional solution of strata deformation induced by foundation pit excavation is obtained based on the superposition principle. Considering the variability of foundation pit shapes in engineering practice, a method for calibrating and categorizing the contact surface between the foundation pit support structure and the strata is proposed. With this method, the shape and size of the foundation pit can be accurately described using only a few specific vectors, thereby greatly simplifying the calculation of surrounding strata deformation induced by foundation pit excavation. Moreover, the entire calculation process has been implemented in a program, and in practical applications, only the input parameters need to be adjusted to assess the strata deformation induced by foundation pit excavation, facilitating its broader application in engineering practice. Finally, using an actual project as a case study, the proposed method was applied and compared with field measurements. The results indicated that the discrepancy between the analytical and measured values remained within acceptable ranges, and the analytical results exhibited good agreement with the observed patterns of strata deformation induced by foundation pit excavation, thereby verifying the reliability of the method. To achieve effective deformation control, measures are recommended to be taken to minimize ground loss and apply pit-bottom loading. The proposed method has a clear theoretical basis, is highly programmable and readily applicable, and provides a practical reference for analyzing and controlling strata deformation induced by foundation pit excavation.