A method and apparatus for automatic gain control of an amplifier in which the method and apparatus detects excessive increase in the sound volume or temperature rise in the audio system and reduces the gain of the amplifier by various means. Each gain control circuit has a comparator to compare a signal with threshold values and an integrator to integrate output signals of the comparator with respect to a predetermined time length to reduce a gain of the amplifier. The method and apparatus conducts dynamic suppressing of excess signals and thereby controlling output level of the amplifier at multiple stages without immediately shutting down the audio system. In the case where the sound volume increases to a degree that may damage the amplifier or speaker, a shutdown signal is generated to shutdown the operation of the whole system.