Abstract: The interaction between fluid and deformable elastic structures encountered in practical engineering is characterized by complicated interfaces between fluid and structure, large free surface deformations, and strong nonlinearities. The improved moving particle semi-implicit method (MPS) is used to simulate the motion of incompressible fluids, and the enhanced bonded particle model (BPM) is introduced to calculate the deformation motion of elastic structures. A new MPS-BPM meshless particle method fluid-structure coupling numerical model based on the pure Lagrangian method is constructed. The model uses pressure gradient forces to quantify the effects of the surrounding fluid on elastic structural particles. By establishing the pressure Poisson's equation for fluid particles and elastic structural particles, a unified numerical discretization solution is performed on the fluid domain and the structural domain to reproduce the feedback effect of the elastic structure on the surrounding fluid. The background grid method is introduced to mitigate numerical pressure oscillations at the fluid-structure interface and the numerical fluctuations of the free liquid surface, thereby enhancing the calculation accuracy and stability of the numerical model. Firstly, the enhanced BPM method is applied to reproduce the response of an elastic cantilever beam to the action of initial instantaneous velocity to verify its accuracy in solving elastic structure deformation problems. After that, the applicability of the MPS-BPM fluid-structure coupling model in simulating complex fluid-structure interaction problems is analyzed by simulating the interaction between dam break flow with elastic gates and the impact of dam break water flow on elastic structures. The calculation results show that the fluid velocity field and pressure field obtained based on the MPS-BPM coupling model change reasonably, the stress distribution inside the elastic structure is smooth, and there is no non-physical gap at the fluid-structure interface. The coupling model can reproduce the motion process of fluid-structure interaction.