In the traditional proportional feedforward grid-connected inverter, the use of multi-resonance control can effectively suppress the background harmonics of the grid and improve adaptability. However, in the case of a weak grid, the grid inductance will greatly reduce the phase margin of the system and cause multiple resonances. The problem is that the resonance peak of the link intersects the 0dB line. Therefore, a combined control strategy of a multi-resonance controller and a phase compensator is proposed. First, a multi-resonant controller is added to the grid voltage feedforward loop to suppress the interference of the grid background harmonics; secondly, in order to solve the problem of adding a multi-resonant controller caused by a limitation in or insufficient system phase margin, a parameter adaptive phase compensator is added to the inverter bridge PWM transfer function to improve that margin. Simulation and experimental results prove that the proposed control strategy can effectively improve the phase margin of the system and enhance the ability to suppress high-order harmonics. This work is supported by the National Key Research and Development Program of China (No. 2018YFC1505502-03), the Project of Chengdu Science and Technology Bureau (No. 2019-YF05-02107-SN), and the Key Research and Development Program of Sichuan Province (No. 21ZDYF3753).