Based on the difference close-loop feedback technique and the difference pre-amp,a high efficiency PWM CMOS class-D audio power amplifier is proposed. A rail-to-rail PWM comparator with window function has been embedded in the class-D audio power amplifier. Design results based on the CSMC 0.5 μm CMOS process show that the max efficiency is 90%,the PSRR is –75 dB,the power supply voltage range is 2.5–5.5 V,the THD+N in 1 kHz input frequency is less than 0.20%,the quiescent current in no load is 2.8 mA,and the shutdown current is 0.5 μA. The active area of the class-D audio power amplifier is about 1.47 × 1.52 mm2. With the good performance,the class-D audio power amplifier can be applied to several audio power systems. Based on the difference close-loop feedback technique and the difference pre-amp, a high efficiency PWM CMOS class-D audio power amplifier is proposed. A rail-to-rail PWM comparator with window function has been embedded in the class-D audio power amplifier. Design results based on the CSMC 0.5 μm CMOS process show that the max efficiency is 90%, the PSRR is -75 dB, the power supply voltage range is 2.5-5.5 V, the THD + N in 1 kHz input frequency is the active area of ​​the class-D audio power amplifier is about 1.47 × 1.52 mm2. With the good performance, the class-D is less than 0.20%, the quiescent current in no load is 2.8 mA, and the shutdown current is 0.5 μA. audio power amplifier can be applied to several audio power systems.