The invention discloses a foundation pit supporting structure. According to the foundation pit supporting structure, a water collection cavity is formed in the face, located above the bottom face of afoundation pit and facing the interior of the foundation pit, of each plate pile; an inclined face is arranged at the bottom of each water collection cavity; a circle of limiting ring is arranged ineach water collection cavity; mounting holes are formed in each limiting ring; a spring is arranged in each mounting hole; one end of each spring is connected with the bottom of the corresponding mounting hole, and the other ends of the springs of each limiting ring are fixedly connected with a division plate; each division plate divides the corresponding water collection cavity into an upper cavity and a lower cavity up and down; the top of each water collection cavity is connected with a vacuum pump communicating with the interior of the corresponding water collection cavity; a draining valve communicating with the interior of the corresponding water collection cavity is arranged on each lower cavity; water collection holes penetrating the two sides of the corresponding plate pile are formed in the face, closely attached to the four walls of the foundation pit, of each plate pile; a communicating hole is further formed in the top of each water collection cavity; and matched reinforcement structures are arranged between the adjacent plate piles. The foundation pit supporting structure has the effects that water in a soil layer is drawn out, the water content of the soil layer is reduced, then lateral pressure borne by the plate piles is reduced, the adjacent plate piles are connected together through the reinforcement structures, and the supporting strength of the plate pilesis increased.