The present invention provides an asynchronous BTL (Bridge Tied Load) design for a Class-D audio amplifier. The Class-D audio amplifier comprises two independent signal routes, each of the two independent signal routes includes a PWM (Pulse Width Modulator), a predriver and a power MOS circuit; each of the two independent signal routes receives an input signal via the PWM thereof, and outputs signal through the power MOS circuit thereof, and then cooperatively drive a loudspeaker; no synchronous signal is inputted to each of the two PWMs, and the two power MOS circuits feed back independent signals respectively to the two PWMs. The present invention omits the synchronous design of the prior art, and let the two push-pull signals required by the BTL design being processed independently, while cooperatively drive the loudspeaker.