In order to reveal the cavitation mechanism of diesel injection process, a numerical model has been developed to investigate the cavitation processes in injector nozzle according to the conservation of mass, momentum and the basic rules of the mixture fraction balance. Then, the numerical simulation results of cavitation effect were analyzed. It is discovered that the atomization performance of high pressure injection nozzle becomes poor and the vapor volume fraction and the thickness of cavitation in the injector nozzle decrease, and the radius of the nozzle inlet rounding lip tends to increase. The numerical study also points out that the amplitude of inlet pressure is reduced with the small variations of outlet mass flow, which is better for the accurate control of injection quantity. The nozzle internal cavitation phenomenon is strengthened at elevated fuel temperature and injection pressure conditions. However, increasing the injection pressure is more conducive to enhancement atomization.