With the deeper development of urban underground space, the deep foundation pit engineering has become an important task in urban construction. When the foundation pit reaches a certain depth, the inrushing problem of the confined water layer will be inevitably encountered. The foundation pit with the suspended water stop curtain is usually required to depressurize as needed during the treatment of confined water layer, which not only ensure the anti-inrushing stability of foundation pit, but also guarantee little influence on the confined water layer out of pit, especially for the complex surrounding environment and high protection level of the foundation pits. The thermal analysis module in ANSYS 10.0 Universal Finite Element Software is used to simulate the process of confined water depressurization in the foundation pit engineering. Then the result of head drop of confined water layer is inherited by the structure module, which is converted into the initial strain of soil layer. Finally, the accurate soil mass displacement result is achieved through the calculation and analysis of structure module, which provides a new method for the design of confined water depressurization of deep foundation pit and the analysis of the influence on the surrounding environment.