The AVL-FIRE software was used to study the effect of water injection to combustion in the YC6G series diesel engine during the intake stroke. Specifically, the influence of intake water injection on engine internal pressure, temperature, emission and ultimately performance was analyzed. Simulation results show that water injection of the supercharged engine has little effect on the average internal temperature and pressure of the engine cylinder but it can still reduce the peak temperature of the cylinder to a certain extent. The effect of water injection at the intake stroke on the exhaust emission is very significant. When the water injection mass fraction increased by 5%, soot production would decrease by approximately 10% and NO_xemissions decreased to 0.21% over when water was not injected. Therefore, the intake stroke boosting water injection effectively improves the combustion inside the diesel engine and reduces exhaust emissions.