Abstract: In this paper, a geometric reconstruction method based on the triangle mesh is proposed to solve the stepped distortion problem of the traditional discrete reconstruction method in the fluid structure coupling numerical simulation based on boundary data immersion method (BDIM), which is combined with BDIM to achieve a high-precision flow field solution, to improve the simulation accuracy of BDIM for complex flow problems. The solid model is reconstructed using the triangle mesh, and the solid is discretized along its approximate normal direction by utilizing the triangle information in the STL file, which effectively avoids the geometric step error caused by discretization along the Cartesian coordinate axis in the traditional method. In this paper, the finite difference method is used to solve the N-S equation, and the Chen cavitation model is used to construct the gas volume fraction control equation. Numerical examples of the flow around a sphere (single-phase) and the Clark-Y hydrofoil (multi-phase) verify the effectiveness of the numerical method. Numerical results show that, compared with the traditional method, the method based on the triangle mesh reconstruction model significantly reduces the distortion of the model surface. For the flow around a sphere at Reynolds number Re = 3700, the proposed method improves the prediction accuracy of the pressure coefficient and the axial velocity distribution compared with the traditional method. After the full development of the flow field, the vortex structure of the flow field around the sphere calculated in this paper is in good agreement with the results obtained by DNS. In the simulation of cavitation multiphase flow around the Clark-Y hydrofoil, the proposed method can more accurately capture the dynamic behavior of the gas-liquid interface. The purpose of this method is to provide a more robust numerical solution for solving complex solid boundary problems based on BDIM while ensuring computational efficiency.