Abstract: In order to study the effect of water injection(WI) on hydrogen engine operation, the AVL-FIRE software was used to simulate the combustion conditions of JH-600 engine using hydrogen fuel. The temperature, pressure, NO emission and other parameters in the cylinder were simulated. The single-cylinder combustion parameters of the engine were calculated in four times, respectively when the WI ratio(mass ratio of water and hydrogen fuel) was 0, 5%, 10% and 15%. The results show that the WI ratio between 5% and 10% can improve the energy efficiency of hydrogen engine and maintain the stable operation of the engine.