Abstract: The interconnection between microgrids through back-to-back converters can realize fault isolation, active and reactive power decoupling control, and two-way power transmission control in the microgrid interconnection system. However, in the back-to-back converters, when one constant power-controlled converter is used as a constant power load, its port impedance will show negative impedance characteristic. This will reduce the stability of the system and cause the system to oscillate. To solve this problem, this paper proposes a coordinated impedance optimized control based on the existing single-impedance optimized control, which improves the system stability by eliminating the phase difference between two ports. Firstly, the structure of microgrid interconnection system and topology and control of back-to-back converters were introduced. Secondly, a small signal modeling of DC side port impedance of bilateral converter under traditional control was constructed to analyze the impedance characteristics. Then, based on the single-impedance optimized control, we analyzed the working principle of coordinated impedance optimized control and remodeled the optimized port impedance. With the minimum loop ratio and the Nyquist stability criterion, we analyzed the system stability under three control system. The results show that the optimized control can make the converters impedance show positive impedance characteristics in the low frequency band, eliminate the phase difference, and make the system have a larger stability margin to maintain better stability. Finally, the effectiveness of the proposed control strategy is verified by Matlab/Simulink simulations and experiments.