Abstract: The power quality of the independent low-power system is closely related to the load characteristics. In the system that the diesel generator set operates alone with pulse load, the output voltage of the diesel generator set is distorted. When the load changes suddenly, the voltage frequency fluctuates greatly, thus it is difficult to obtain the fundamental frequency and extract each harmonic effectively. In this case, it is useless to measure the distortion rate of voltage using the total harmonic distortion (THDv). Hence, a method measuring the distortion rate of voltage under the action of the pulse load, namely distortion rate of voltage (DRV) is presented. By testing the experiment system of the diesel generator set working with the pulse load, and comparing THDv with DRV in different operational modes, the method proposed in this paper is verified to be reasonable. At this base, the influence law of pulse load working mode and the generator output power to the DRV is obtained.