Abstract: In order to take account of pressure fluctuation impact on cavitation inception, the instantaneous flow field inside a high-pressure diesel nozzle was investigated by a large eddy simulation method with a dynamic subgrid-scale stress model. The results show that time-averaged turbulent fluctuated pressure can reach up to twice as much as the time-averaged static pressure within the local low pressure area induced by inlet flow separation. The time-averaged location and shape of cavitation inception calculated by two-phase simulation is in a good agreement with the experimental results, which is also consistent with the cavitation inception zone predicted by time-averaged static pressure and turbulent fluctuated pressure. The instability of a separation shearing layer leads to the formation of a large-scale cylindrical vortex and triggers the laminar-turbulent transition process. Within the separation transition zone, the cylindrical vortex distorts, accompanied with intense instantaneous pressure fluctuation which results in cavitation. Further, the inlet filleting reduces a flow separation and has a suppressive effect on the transition process and cavitation inception.