In order to explore the mechanical characteristics and the pore water pressure distribution law of the prefabricated subway station during the construction process，taking the Jieda Road Station in Changchun Subway Line 2 as the background and by using FLAC^3D numerical simulation software，the mechanism of the prefabricated subway station construction process was studied in this paper. The research results show that：Under the influence of the gravity of the ground wall and the station，the station structure will produce horizontal lateral displacement and settlement to the interior of the foundation pit；The maximum settlement occurs at the station floor，and the maximum horizontal lateral displacement occurs at the top of the side wall. During the station assembly process，the maximum Mises equivalent stress appears at the arched area of the floor，the middle slab，and the outside of arch foot’s bottom plate. As the number of station rings increases，the maximum Mises equivalent stress also increases.After backfilling the overlying soil，under the action of the water pressure difference between the inside and outside of the pit，the groundwater bypasses the ground wall and flows to the bottom of the foundation pit，causing leakage at the joints of the station floor；As the pore water pressure reaches a balanced state，the change of pore water pressure at the joints gradually stabilized.