The invention discloses an audio frequency PWM modulation circuit comprising a main power supply voltage input end, a working voltage input end, an audio frequency signal input end, an audio frequency PWM modulation signal output end, a main power supply voltage compensation circuit, a sawtooth wave generator circuit, and an audio frequency PWM comparator circuit. The sawtooth wave generator circuit is used to generate sawtooth wave voltage signals. The audio frequency PWM comparator circuit is used to generate reference voltage signals, is used to compare the reference voltage signals with the sawtooth wave voltage signals to generate the PWM modulation fundamental wave signals, and then is used to modulate the audio frequency signals of the audio frequency signal input end to acquire the audio frequency PWM modulation signals. The audio frequency PWM modulation signal output end is used to output the audio frequency PWM modulation signals to the power driving module of the power amplifier. The main power supply voltage compensation circuit is used to stabilize the output power of the power driving module of the power amplifier. The output power of the power driving module of the power amplifier can be stabilized.