In order to ensure the symmetrical output current of PV grid-connected inverter under Unbalanced Voltage Condition,in this paper,the mathematic model of PV grid-connected inverter under unbalanced voltage condition is given,and the disadvantages of conventional PI strategy in the synchronous rotating reference system are discussed.A improved dq-PI Control Strategy is proposed based on the research of dual dq-PI controller in the synchronous rotating positive/negative reference system.Compared with the conventional PI control strategy and improved dq-PI control strategy based on PSCAD,the simulation results verify that the proposed strategy could keep current balance of PV inverters.