A distortion compensation method for a class-D audio amplifier has the steps of connecting a compensation circuit to the class-D audio amplifier; providing a feed-forward signal from the compensation circuit to the loop filter, wherein the feed-forward signal contains replicate high-frequency components replicated from original high-frequency components of the class-D audio amplifier; and adding the feed-forward signal to those of the class-D audio amplifier. By adding the feed-forward signal, PWM-intermodulated distortion resulted from the high-frequency components is reduced. The class-D audio amplifier still maintains loop stability without affecting its phase margin.