This paper focuses on the stability of modular multilevel converter（MMC） using virtual synchronous generator（VSG） control. Firstly

based on the idea of modular modeling

an accurate small-signal stability analysis model of MMC using VSG control is established. Then

the eigenvalues of the two-level simplified model is compared with that of the accurate MMC model

revealing that the simplified model ignores a coupled mode（about 16 Hz） which is affected by both VSG control and circulating current suppression control（CCSC） parameters. Thirdly

the stability of three important modes of external mode（about 2 Hz）

coupled mode and internal harmonic mode（about 100 Hz） is analyzed. The stability analysis results show that adjusting the VSG control parameters will increase the damping and stability of external mode and reduce the damping and stability margin of the coupled mode. Therefore

it is necessary to pay attention to the stability of the external mode and coupled mode when optimizing the VSG control parameters. In addition

external mode instability may occur when the power grid is weak

and internal harmonic mode instability may occur when the CCSC parameters are unreasonable. Finally

the stability is compared to that of classical vector control

revealing that there exists no coupled mode under classical vector control

thus the stability of VSG control is better when the power grid is weak.