A power conversion system with zero-voltage start-up mechanism and a zero-voltage start-up device are disclosed. The system includes a power conversion circuit, a power factor correction unit, a storage capacitor, a storage switching unit, and a zero-voltage detection module. The storage switching unit is serially connected with the storage capacitor, and particularly controlled by the zero-voltage detection module. The zero-voltage detection module detects a timing as an input voltage is at low level, and then outputs a control signal to turn on the storage switching unit. Therefore, the present invention assures that the power conversion system is turned on when the input voltage is at the low level, in order to suppress the system from a surge current.