The erosion mechanism and deformation characteristics of rhomboid-shaped particle impacting metal beam are studied. Physical experiments of rhomboid-shaped particle impacting cantilever beam and fixed-fixed beam are carried out respectively. The erosion behavior of particles and deformation characteristics of beam are captured by high-speed imaging system. Meanwhile, the numerical models of rhomboid-shaped particle impacting beam, based on FEM-SPH coupled method, are established. The effects of the geometrical parameters of the beam, the incident conditions of particle and the impact position on the elastic-plastic deformation of beam and rebound behavior of particles are further analyzed. The results show: (1) The width of cantilever beam affects its maximum deflection and deformation; (2) The threshold value of breakdown velocity is controlled by the substrate size; (3) The increment of internal energy is basically independent of the impact position; (4) The deflection value at impact position of beam is maximized under the critical impact condition.