17℃。 The numerical simulation and steady flow testing approach were applied to the design of diesel engine air-intake ports. Furthermore, by using forward design and reverse engineering, the intake ports have been developed which were suitable for the variable swirl system of a diesel engine with bore diameter 132 mm. The models and moulds of the intake ports were machined by the method of rapid prototyping and numerical control machining. Subsequently, sand core moulds of an intake ports have been made, and cylinder head has been molded. Some tests were completed on a single-cylinder diesel engine. The results showed a remarkable performance improvement has been reached that fuel consumption decreased 7.1 g/(kW?h), the emission of soot decreased by 50% and the temperature of exhaust decreased to 17℃.