The invention provides an audio power amplifier provided with a double-power amplifying module. The audio power amplifier is characterized in that a backup module can be directly switched in case of fault occurring in some module inside, so that the continuity and the safety of a broadcasting system can be ensured. The condition of no fault can be fed back or the fault information can be directly displayed during the detection of each module, the startup self-inspection and the full-load detection, and the logging is carried out for inquiring or further treatment. A detection signal can be automatically sent through the audio power amplifier and used for quickly detecting the power amplifying module; the automatically-sent detection signal is sine wave of which the frequency ranges from 20Hz-20kHz, and the sine wave is generated through a sine wave signal generation unit 45; the sine wave of the frequency is 1kHz is treated as a detection signal optimum scheme. According to the audio power amplifier, the signal is subjected to grain adjustment through a digital pre-amplification unit 44 before being input to the audio power amplifying module, so that the signal attenuation which influences the detection can be prevented; in addition, the grain adjustment of the digital pre-amplification unit 44 to the detection signal is variable, and the grain value is determined according to the power amplification output value.