A power conversion system including a power conversion unit, a power circuit and a precharge circuit is provided. The power conversion circuit includes an input port, an output port, switching power conversion units and at least one storage device. The storage device is connected between the input and output ports in series. The power circuit is electrically connected to the power conversion circuit for receiving the input voltage and outputting a supply voltage to the power conversion circuit, and the power circuit includes a magnetic element. The precharge circuit precharges the storage device. The precharge circuit includes a winding and a rectifier filter circuit connected to each other. The winding is coupled to the magnetic element for receiving a conversion voltage. The rectifier filter circuit is electrically connected to the storage device so as to receive the conversion voltage and output a charge voltage to the corresponding storage device.