Aiming at the problems of low fuel injection pressure and inability to flexibly change the fuel injection rate in the injection process of conventional high pressure common rail system, an ultra high pressure common rail system for adjustable fuel injection rate based on domestic processing capacity and technology was proposed and designed. On the basis of introducing the working principle of this system, the simulation model of system was established via AMEsim software, the accuracy of this model was verified by experiment, and the pressure characteristics and fuel injection control characteristics of the system were studied through the model. A at the same time, the influence of the key structural parameters of the electric-controlled pressure amplifier on the system performance were analyzed. Results show that the ultra high pressure common rail system for adjustable fuel injection rate can magnify fuel pressure to the ultra high pressure state, and by changing the control signal working time of electric-controlled pressure amplifier and injector solenoid valve in system, the flexible and controllable fuel injection rate curve shape can be achieved. Compared with the control chamber volume and spool mass, the fuel outlet diameter and spool displacement have greater influence on the performance of this system, with the increase of fuel outlet diameter and spool displacement, the pressurization pressure and fuel injection rate peak value both increase, while the fuel leakage rate increases first and then decreases.