In photovoltaic (PV) grid-connected system based on series-connected power optimizer, the open-circuit fault of the inverter will seriously affect the security and reliability of system operation. To solve this problem, two kinds of open-circuit fault detection methods for the inverter based on series-connected power optimizer without communication are proposed. Firstly, the fault detection method based on charge change rate and power change rate is proposed separately. Then, the defects based on the charge judgment and the improvement based on the power change rate are analyzed. Finally, the effectiveness and reliability of the proposed method are verified by experiments.