For the problem that the actual injection pressure of injector could not be directly achieved in the test, the fuel injection law of common rail injector matching with different nozzle orifices was acquired through the HDA injector performance test equipment and the average injection pressure and the maximum actual injection pressure under different nozzle orifices were acquired through the calculation. The analysis results showed that the pressure drop of fuel groove at the initial stage of injection was not conducive to quick opening of needle valve. In addition, reducing the length of the fuel pipe between fuel rail and injector could accelerate the pressure recovery of fuel groove and increasing the ratio of fuel return orifice and fuel inlet orifice in control chamber could improve the response of needle valve and even improve the utilization efficiency of highpressure fuel in fuel groove so that the maximum and average fuel injection pressure increased by 70% and 75% respectively and the cyclic fuel injection quantity increased by 34%.