Abstract: Small signal model is a general and important method to implement stability analysis and control parameters design. At present, on the small signal modeling of the modular multilevel converter（MMC）, the internal dynamics including the sub-module capacitor voltage fluctuations, the inner loop current, the loop current controller are often neglected, thus simplifying the state-space model, but bringing in some errors for the eigenvalues and stability analysis. A detailed small-signal model of the MMC with consideration of the internal dynamics of the converter was developed. The developed model provides convenient interface with the outer controller and the AC and DC system. The dynamics evaluation with this model was compared with a detailed electromagnetic transient simulation model, and the correctness of the model was validated. Besides, the small signal model of a simplified terminal model was also established and compared with the detailed MMC model. It is demonstrated the simplified model can not evaluate some instability phenomena accurately and the establishment of a detailed MMC model is necessary.