The output characteristics of power electronic transformer output stage inverter and off-grid inverter in micro-grid are directly affected by loads. AC loads usually contain a large number of nonlinear and unbalanced mixed loads, which will cause harmonic distortion and imbalance of three-phase inverter output voltage. Aiming at solving those problems, a hybrid control strategy of three-phase four-leg inverter is proposed for unbalanced voltage compensation and harmonic suppression. Firstly, the coupling relationship among the four legs is clarified, which is based on the mathematical model of the four-leg inverter. Then, the requirements for eliminating AC signal tracking error and suppressing harmonics are analyzed in detail. Meanwhile, the effectiveness of the proposed control method and parameter selection is illustrated by analyzing the amplitude-frequency characteristics of bode diagram. Finally, the correctness and validity of the proposed control strategy and selected control parameters for the inverter with nonlinear and unbalanced mixed load is verified by the simulation results in αβ0 frame.