Abstract: The modular multilevel matrix converter (M³C) has a complex topology and double-fundamental-frequency electrical coupling characteristics, and there is a lack of effective modeling methods to analyze the coupling mechanism of the double-fundamental-frequency harmonics. Firstly, considering the independence between the frequencies of the fractional frequency transmission system, we propose a novel double-fundamental-frequency dynamic phasor method based on the two-dimensional Fourier transformation theory. The method can achieve the decomposition of the double-fundamental-frequency harmonics on the two fundamental frequency spectra. Secondly, a double-loop control system is modeled based on the dynamic phasor frame, and then a dynamic phasor model with the 3^rd-order harmonics truncated and a small-signal model are created after taking into account the closed-loop control system. Finally, based on the MATLAB/Simulink environment, simulation verification is conducted at three operating points with different frequency and power commands. The results show that the model has high accuracy, and the errors mainly come from the higher harmonics that the model fails to cover. Besides, the correctness of the proposed modeling method is further verified by the analysis results of dynamic and steady-state characteristics of the model.