Abstract: The effect of difference scheme on the simulation results of intake flow in a diesel engine was studied.The three-dimensional simulation of intake flow of a double-intake-port diesel engine was performed by using a three-dimensional software FIRE.Various difference schemes were used to solve the momentum equation,continuity equation and turbulence equation.The computed mass flux and the swirl rotate speed were compared under different conditions.And the computed results were compared with the experimental results.Results indicated that the differences among the computed values of mass flux under the condition of various schemes are very small.But,the differences among the computed values of swirl rotate speed under the condition of various schemes are very big.When the high order difference schemes and appropriate blend factor are adopted,the errors between the computed results and experimental results will be very small.