Numerical simulation of Fluid-Structure Interaction (FSI) has long been an active research topic. The main challenge is that fluids and solids have very different deformation modes and stress update methods, making it difficult to analyze their coupled behavior within a single numerical framework. To simplify the calculation process, this study aims to build a unified numerical framework for FSI analysis. The numerical method employed in this research is the Material Point Method (MPM) [1,2]. MPM integrates the advantages of both Eulerian grid-based methods and Lagrangian particle-based methods, effectively overcoming the limitations of mesh distortion in large-deformation problems. Furthermore, the procedure for updating the stress tensor via the strain rate tensor in MPM is inherently consistent with fluid dynamics formulations. Consequently, MPM has been previously applied to large-scale FSI problems, such as dam-break simulations. However, the application of MPM to micro-scale FSI problems—such as the impact of a water droplet on a flat plate—remains relatively limited. To address this gap, the present study utilizes MPM to simulate the behavior and interaction of a water droplet, with a diameter of only 3 mm, during a vertical impact onto a plate. The simulation results are first validated against experimental data obtained from high-speed camera recordings of the impact process. Subsequently, by varying the boundary conditions and geometric settings, this study investigates their effects on the deformation of both the droplet and the plate. Finally, by adjusting the constitutive laws of the droplet, the differences between compressible and incompressible fluid stress update mechanisms within the MPM framework are explored. REFERENCES [1] D. Sulsky, Z. Chen, and H.L. Schreyer, Computer methods in applied mechanics and engineering, 118(1-2), 179-196, (1994). [2] X. Zhang, Z. Chen, and Y. Liu, (2016). The material point method: a continuum-based particle method for extreme loading cases, Elsevier Science, 2016.