An engine piston is provided. A first sealing structure, including a first sealing rubber ring and a first annular groove, is provided at a head of the engine piston. The first sealing rubber ring has a U-shaped section with a reserved space at the top of the first sealing rubber ring, and a gap for circulating hydraulic oil is provided between a ring bank, above the first sealing rubber ring, of the engine piston and a simulated cylinder liner of a fatigue testing apparatus for an engine piston. In a case that the hydraulic oil is introduced into the fatigue testing apparatus for the engine piston to simulate pressure loading under a high-explosion pressure, when the hydraulic oil enters into the reserved space from the gap for circulating the hydraulic oil, an inner wall of the reserved space is squeezed and the first sealing rubber ring is deformed.