A power conversion device and a method for preventing abnormal shutdown thereof are provided. The method includes: providing a power conversion device including a main power supply and a standby power supply electrically connected to the main power supply. The standby power supply is configured to provide an operational voltage for microcontrollers of the main power supply; performing a monitoring procedure for monitoring the operational voltage when the power conversion device entering a non-standby mode and the standby power supply is inactivated; and forcing the standby power supply to activate before the operational voltage is lower than a preset compensation voltage, such that an abnormal shutdown condition of the power conversion device while the operational power is equal to or lower than the preset compensating voltage is prevented.