A micro-inverter could be directly integrated with a PV panel to generate grid-compatible AC power. Placing two flyback converters in parallel as the DC-DC stage and utilizing interleaving extends the power range of flyback micro-inverters. In this paper, open-loop interleaving technique for flyback micro-inverter operating at the boundary conduction mode (BCM) and discontinuous conduction mode (DCM) with a master-slave relationship are analyzed first. Then, a novel interleaving phase synchronization control method is proposed to achieve high power conversion efficiency and stable operation at the same time. In DCM operation region the open-loop phase regulation will be utilized while in BCM a closed-loop technique will dominate. A 200 W interleaved flyback micro-inverter prototype is built to verify the proposed interleaving synchronization control method. Simulation and Experimental results are provided to show that the proposed closed-loop control method could achieve stable interleaving phase synchronization while maintain good efficiency and low THD performance.