Accurate injection timing is necessary for the coordination of fuel injection system, intake system and combustion chamber. However, the electric unit pump has obvious delay characteristic, so the delay characteristics of electric unit pump were studied in this paper. Five main parameters of the delay characteristics were defined, which were namely electronic delay, electromagnetic delay, electro hydraulic delay, hydraulic delay and mechanical delay. Then six delay points were determined such as current generation delay, solenoid valve closing delay, injector opening delay, injection delay, solenoid valve opening delay and fuel pressure relief delay by analyzing the working process of the system. Based on the method of experiment, the change rules of the delay time were obtained at different input conditions by changing the parameters of cam speed, injection pulse width, injection timing, peak current and holding current finally. The result shows that the injector opening delay time decreases, the fuel pressure relief delay time increases and the other delay times remain steady as the cam speed increases. The fuel pressure relief delay time increases and then decreases, the other delay times remain steady in the range of injection pulse width 8~15°CAM. The injector opening delay time decreases and then increases, the fuel pressure relief delay time increases and the other delay times remain steady in the range of injection timing −8~8°CAM. The solenoid valve closing delay time decreases, the injector opening delay time and the fuel pressure relief delay time increases, and the other delay times remain steady as peak current increases. The solenoid valve opening delay time increases and the other delay times remain steady as holding current increases. The results provide a reference for precise control of injection timing.