A control strategy based on peer-to-peer structure is proposed, so as to realize stable operation and smooth transition between grid-connected and islanding modes of microgrid. In stable operation mode, the multiloop control strategy includes voltage-phase droop control, virtual impedance control and voltage-current dual loop control. According to the ratio of the rated capacity of the inverters, the load power can be precisely distributed. Also, it can maintain the voltage amplitude and frequency of the system. In grid connecting transition mode, a voltage synchronization strategy is proposed. It is based on dual second-order generalized integrator and frequency locked loop, which synchronizes the voltage amplitude and phase of microgrid with the main grid in a short time, so that it can be connected to the main grid smoothly. In grid disconnecting transition mode, a power synchronization strategy is proposed. The overshoot of power is suppressed by reducing the interaction power between the microgrid and the main grid. The simulation results show that the proposed control strategy can maintain the stable operation of the microgrid. Also, when modes switching, it can reduce the overshoot in the grid and control the frequency of the system, so as to realize mode smooth transition. This work is supported by National Science and Technology Support Project of China (No. 2015BAG19B02) and Project of Shanghai Committee of Science and Technology (No. 13DZ1200403).