A method of controlling phase shift pulse width modulation of a power converter, the method includes a step of obtaining sampling signals of an output voltage and current of the power converter. Then, a digital signal processor is used to calculate an output power of the power converter. Next, a comparator is used to compare the output power of the power converter with a reference power. When the output power is less than the reference power, the modulation control of the switch of the power converter enters into hard-switching mode, and when the output power is greater than the reference power, the modulation control of the switch of the power converter enters into soft-switching mode.