Abstract: A catapult experimental device was designed to study the impact behavior and erosion mechanism of rhomboid particles impacting on metallic surfaces. Through the observation by high-speed camera, the motion trajectories of particles at different impact velocity v_i, impact angle α_i and orientation angle θ_i were captured. A coupled numerical model (FEM-SPH) based on Lagrange method was established to deeply analyze the impact behavior of angular particle and deformation of crater profile. The results show that the initial orientation angle θ_i, and the impact angle α_i, which were the major factors, determined the erosion mechanism. For agiven impact angle α_i, there existed a critical orientation angle θ_cri; if θ_i<θ_cri, the particle tumbled forwards, while for initial orientation angles θ_i>θ_cri, the particle tumbled backwards after the impact. It also has been revealed that the rotation of particle highly influenced on the erosion mechanism. For example, a forwards rotating particle usually resulted in " ploughing” action, while " machining” action can be observed in a backward impact process. In addition, the impact angle α and orientation angle θ had a great influence on kinetic energy loss of particle. In general, impacts at critical initial orientation corresponded to the peak value of kinetic energy loss.