An experimental study was carried out on a 3.8 L turbocharged inter cooled diesel engine to reveal the influences of intake pressure on the performance of the engine. In the experiments， the turbocharger and intercooler of the engine were removed and the intake and exhaust pressures of the engine were controlled directly by a self made pressure control system. The experiment and simulation results show that when the exhaust back pressure is kept constant， the maximum cylinder pressure is in linear relationship with the intake pressure， and the maximum cylinder pressure rises by 4.8~7.0 MPa every time the intake pressure increases by 100 kPa. The corresponding crank angle of the maximum cylinder pressure has no clear relationship with the intake pressure. The mass flow rate is in linear relationship with the intake pressure， and the mass flow rate goes up by 13~37 kg/h every time the intake pressure increases by 10 kPa. The exhaust temperature has obvious linear relationship with the air to fuel ratio， and the exhaust temperature decreases by 4.2 ℃ every time the air to fuel ratio increases by 1. With the increase of the intake pressure， the ignition delay will be smaller， the combustion starts earlier， but the combustion duration has no clear change. The brake torque of the engine will increase by 0.8~2.5 N·m every time the intake pressure increases by 10 kPa.