Abstract: The direct power injection method was used to study the effect of electromagnetic interference coupling on the power supply of typical audio power amplifier circuits. The electromagnetic interference coupling characteristics of typical audio power amplifier circuits were analyzed. The electromagnetic interference test platform based on the direct power injection method was designed to test the electromagnetic interference effect on the DC power signal of the circuit in the range of 0.1-1 GHz. The power thresholds for the critical distortion, typical distortion and full distortion of the circuit and their laws with the interference frequency were obtained. The results show that in the test frequency band, the distortion power threshold has the same relationship with the frequency under the three distortion states, and the difference of distortion power threshold is about 2 dBm. When the injection interference frequency is lower (100-300 MHz), the distortion power threshold is higher, and decreases with the increase of the frequency in the trend of power function approximately. When the injection interference frequency is higher than 300 MHz, the distortion power threshold tends to damped oscillation with the increase of the frequency. The use of electromagnetic interference can affect the normal operation of audio electronic devices, which provides a new thought for the study on ultra-wide spectrum electromagnetic interference effects of audio integrated circuits.