As one of the core components of the rock drill, the impact piston has significant effects on the percussion capabilities of the rock drill. During its operation, failure phenomena such as rod body fracture, fatigue spalling, and working surface scratching often occur. Through the transient collision dynamics analysis and the failure analysis of the fractured impact piston, the failure mechanism of the fractured impact piston is revealed. The results show that when the impact piston is working, it is affected by a large eccentric force, causing the gap between the working surface of the piston and the mating surface to disappear and the oil film to be damaged. As a result, the working surface of the impact piston wears and deforms, becoming a stress concentration area and the origin point of cracks. The hardness of the material's core part is excessively high, while its toughness is extremely low, which cannot form a strong stress release area at the front of the crack to hinder the crack propagation. The crack propagation rate is so fast, resulting in a short service life of the impact piston.