The combustion of diesel engines is mainly controlled by fuel injection. Determining the fuel injection flow rate combined with the common-rail fuel injection system is a key solution to effectively improve engine performance and exhaust emissions. This work aims to investigate the influence of high injection pressures with a 6-holes-solenoid common rail injector on the injection rate characteristics in the range of 400 bar to 1600 bar, and a constant injector energizing time of 1.5 ms. The injection rate characteristics were carried out based on the pressure difference in the Zuech measuring chamber and synchronized data in real-time. The results showed that the increase of the mentioned injection pressures caused the decrease of hydraulic injection delay from 0.5 ms to 0.25 ms and expansion of the injector opening angle profile. In addition, the actual opening injection interval was prolonged as compared to the injector control signal. An increasing trend of fuel discharge coefficient was realized as higher injection pressure.