Abstract: This paper introduces a geometric reconstruction method based on triangle mesh to address the issue of staircase distortion inherent in traditional model discretization techniques for fluid-structure interaction (FSI) numerical simulations utilizing the Boundary Data Immersion Method (BDIM). By integrating this method with BDIM, high-precision flow field solutions are obtained to enhance the simulation accuracy of BDIM for complex flow scenarios. By leveraging the triangular facet information contained within the STL file, the solid is discretized along its approximate normal directions, thereby effectively mitigating the geometric staircase errors that arise from discretization along Cartesian orthogonal axes in traditional approaches. The efficacy of the proposed method is demonstrated through case studies involving single-phase flow around a sphere and multiphase flow with cavitation around a Clark-Y hydrofoil. The results indicate that, compared with traditional methods, the triangle mesh reconstruction method significantly reduces the distortion of the model surface. Specifically, for flow around a sphere at a Reynolds number of Re=3700, the proposed method exhibits improved prediction accuracy for the pressure coefficient and axial velocity distribution. Furthermore, in simulations of multiphase flow with cavitation around a hydrofoil, the method presented in this paper more accurately captures the dynamic behavior of the gas-liquid interface. This method aims to provide a more robust numerical solution for complex solid boundary problems based on BDIM, while ensuring computational efficiency.