For the current simplified calculation of pile-brace support structure can not calculate the displacements of pile and brace, the authors try to start from the deflection differential equation of beam on elastic foundation, considering the deformation compatibility of pile and brace, and obtains the internal forces and displacements of pile by using Finite Difference Method. Meanwhile, Finite Element Method is used to analyze and calculate the horizontal displacements of pile. The results show that the values obtained by this article are closer to the measured values than that obtained by Finite Element Method. The method is accurate, reliable and simple. Besides, this author also analysis the different horizontal displacements of pile under different parameter conditions of support structure, which can provide some valuable suggestions for the design of foundation pit.