The photovoltaic power source would keep supplying power under unscheduled islanding operation, and hence bring potential risk for maintenance personnel and electric equipments, so it is of great significance to enforce accurate and rapid islanding detection method. A method based on negative sequence current injection and voltage imbalance on the point of common coupling is proposed. The reasonable switching strategy of negative sequence current in the grid-connected inverter reduces the impact of injected current on the main power grid. The method, without non-detection zone, is also unaffected by asymmetric faults of the power grid. Case study shows that the method could detect islanding state accurately and quickly under the worst condition while the power of the PV matches the load power, and the voltage and the frequency of the PCC has small shift.