A power conversion system mainly includes an input capacitor bank, a first conversion circuit, a second conversion circuit, and a control circuit. The input capacitor bank has a first capacitor and a second capacitor. The first capacitor and the second capacitor are connected to a neutral point and receive a DC input voltage. The first conversion circuit is connected in parallel to the input capacitor bank, and has a first branch, a second branch, and a first auxiliary branch. The second conversion circuit is connected in parallel to the input capacitor bank, and has a third branch, a fourth branch, and a second auxiliary branch. The control circuit produces a plurality of control signals to correspondingly control the first conversion circuit and the second conversion circuit so as to reduce leakage current caused by parasitic capacitance voltage.