Gasoline direct injection requires that the injection time may be very short in duration, indicating that transient flow effects can have a strong influence on the flow behavior and on the spray properties. Consequently, a computational analysis of the dynamic flow in a high pressure swirl injector was conducted. In order to perform the flow simulation during a complete injection event, movement of the needle that controls the amount of fluid to be discharged has been considered and deduced from experimental data.To validate the computational model, the predicted dynamic flow rate, temporal cone angle and instantaneous mass flow rate were compared to experimental data. The calculated results were found to be consistent with measurements.The dynamic calculations allow a better understanding of the complex transient flow during one injection event and may be divided into four different stages where characteristics of the liquid emerging from the nozzle are completely different. In this paper, an attempt for determining the volume of fuel supplied during each stage is proposed.