Based on a deep foundation pit supported by piles and anchors in Shenzhen, the HS model of PLAXIS software was used to calculate the dewatering excavation process of deep foundation pit, and the law of deformation changing with time in dewatering excavation process was obtained. On the premise of considering time change, the calculation results of deformation and internal force of supporting structure of deep foundation pit with and without considering fluid structure coupling were analyzed. The results show that: (1) the horizontal displacement of the pile and the surface settlement outside the pit produce a rebound phenomenon during the consolidation period set after the excavation, and the pit bottom uplift after the consolidation period increases compared with that after the excavation; (2) the horizontal displacement of the pile and the settlement of the ground surface of the outside pit increase significantly when considering the fluid solid coupling compared with that without considering the fluid solid coupling. The vertical displacement of the pile has the same effect on the deformation of the soil at the bottom of the pit, and the pile has a limiting effect on the uplift at the bottom of the pit; (3) the bending moment of the pile above the bottom of the pit is larger when considering the fluid structure coupling, while the part below the bottom of the pit is just the opposite; in addition, the final axial force when considering the fluid structure coupling is smaller than the final axial force when not considering the fluid structure coupling.