The invention provides a grid-connected inverter circuit and a control method thereof. The grid-connected inverter circuit comprises an inverter, an (N+1)-port transformer, a 2N-phase rectifier, 2N voltage dividing capacitors and a (2N+1)-end inverter; direct-current voltage is subjected to high-frequency inversion via the inverter to generate high-frequency square wave, the high-frequency square wave passes through the (N+1)-port transformer to boost the voltage into voltage of N voltage levels, the square wave of the N voltage levels is respectively rectified to form voltage of 2N different levels, the voltage of 2N different levels and a zero potential grounding point form (2N+1) level branches, the levels are isolated by the capacitors connected in series longitudinally and charge the capacitors, and the (2N+1) level branches are respectively connected with the (2N+1)-end inverter. The whole circuit adopts multi-level inversion, so that the content of output harmonic is greatly reduced, additional high-capacity filters are not needed, and the structure is simple.