The present invention provides a power switch series circuit and its control method. The power switch series circuit includes a plurality of series modules, a control module and a drive module. At least one series module has a power switch and a detection module, and the detection module includes a detection unit and an isolation unit, so as to detect the overvoltage and output a voltage detection signal based on the detected voltage. The control module receives the voltage detection signal and outputs the corresponding control signal. The drive module amplifies the control signal to drive each power switch to turn ON or turn OFF. The control module outputs the corresponding control signal to turn off each power switch when the overvoltage happens.