With the control of the pressure,timing and rate of fuel injection,high pressure common-rail injection system can improve the whole performance of diesel engine,so it is regarded as the most potential electronic controlled system for diesel engine.On the basis of deep discussion about emission and demand on the injection system,the construction of high pressure common-rail injection system and the performance improvement of diesel engine in the case of ECD-U2 system,especially its function of emission control are analysed.Applications of this system are also introduced.