During the functionality experiment of the electrically controlled injection system of high pressure common rail diesel engine, the special relationship between injection time gap and corresponding injection quantities was summed up on the basis of analysis on the experimental data. Based on the investigation of current pulses acting on the solenoid valve, and on the analysis of the kinematical models for solenoid valve shutter and injector needle, the relationship mentioned above was explained theoretically. Finally, this paper has made the conclusion of the whole tendency of injection quantity varies with the time gap which is between pilot injection and main injection. This provides a convincing experience for the following calibration experiment on diesel engine, and a reliable reference for further research work on electrically controlled unit (ECU) of the high pressure common rail injection system.