The deformation of the surrounding underground pipelines caused by the foundation pit excavation needs to be paid more attention to when the scale of infrastructure continues to expand nowadays. First, additional stress on adjacent pipelines caused by foundation excavation was calculated. Then the equilibrium differential equation of vertical displacement of underground pipeline was established using two-stage method based on the Pasternak foundation model, and the finite difference method was used to obtain the matrix analytical solution in the most concise form. Finally, the theoretical calculation results were compared with the monitoring data recorded in the two engineering cases. It shows that the calculation results almost matched the monitoring deformation law of underground pipelines, which validated the feasibility and accuracy of this method. The calculation model, which is high in accessibility of the concept and also concise and explicit when referring to the calculation result, may be implemented as a new method to analyze and predict the impact of foundation pit excavation on adjacent underground pipelines.