Abstract: A thermodynamic model of a V-type turbocharged multi-cylinder diesel engine was established and calibrated by its experimental data. Then, the non-uniformity of intake air flow on ring-type intake pipe and Π-type intake pipe was respectively investigated depending on this model. The computed results indicated that various intake structures came into being various pressure fluctuation rule of the intake air flow in front of the valves. Furthermore, the variety of pressure difference between the intake air and in-cylinder air was generated which is the main reason of largely different degree of intake air non-uniformity. The conclusion is that the non-uniformity of intake air flow of engine could be reduced by using ring-type intake pipe.