The relationship between injection pressure fluctuations and unsteady cavitation processes inside the high-pressure diesel nozzle holes have been numerically analyzed by using a two-fluid approach. In order to improve prediction of nozzle hole cavitation content under high-pressure injection conditions, a new adjustment model of bubble number density has also been developed through the analysis of cavitation bubble dynamics and internal flow characteristics of nozzle hole. Model validation results verify that this model is applicable for a wide range of diesel injection pressures. Based on simulation results, it has been found that cavitation bubbles in recirculation zone and its wake flow show totally different responses to the variations of upstream pressure, and the evolution of cavitation content shows a close association with the time derivatives of upstream pressure. (C) 2010 Elsevier Ltd. All rights reserved.