Abstract: Multiple-injection quantities including main injection and pilot one were simultaneously measured by the instantaneous mono-injector qualifier, which was supplied by the French company EFS. Based on the analysis of the amount of the experimental results, the paper concluded the changing tendency of the injection quantities along with the decrease of injection interval(the time gap between the pilot and main injections). Furthermore, the main injection quantity was found remarkably vibrating on the small interval condition, and the electro-hydraulic delays of the injector, together with the fuel pressure fluctuation at the moment of the interval were validated to be the main causes. This research contributes to providing a reliable reference for calibration and software design for the electronically controlled high pressure common rail injection system.