A MOS transistor-driven undervoltage protection circuit in a high-power switch amplifier At one end of that pow supply V1 in the circuit, At that other end of the pow supply V1 is connected to the collector of the transistor Q4, The 1 port of the digital optocoupler U1 is connected to a voltmeter V2 through a resistor R10, Voltmeter V2 is connected to port 3 of digital optocoupler U1, the 5-port of the digital photocoupler U1 is connected to the collector of the transistor Q4, At the same time, the five ports of the digital photoelectric coupler U1 are connected to a resistor R11 through a resistor R7, the 4-port of the digital photocoupler U1 is connected to the base of the transistor Q6, The collector of the transistor Q6 is connected to the resistor R11, the emitter of the transistor Q6is grounded, the resistor R1 is connected to the base of the transistor Q2, and the resistor R1 is connected to the diode D1 through the resistor R2. The MOS transistor driving under-voltage protection circuit in the high-power switching amplifier designed by the invention has the advantages of low cost, low power consumption, high reliability, safety and reliability.