The work aims to further improve the protection performance of Mg-rich coating on magnesium alloy on the condition of ensuring the cathodic protection and decreasing content of the magnesium powder. Firstly, graphene modified Mg-rich coating were prepared by adding different mass fractions of graphene (1wt%, 2wt% and 4wt%) to Mg-rich coating to replace part of the magnesium powders. Then, the protection performance of different graphene modified Mg-rich coatings was studied by Machu test, electrochemical impedance measurement (EIS), open circuit potential (OCP) and scanning electron microscopy (SEM). The results show that the addition of excessive graphene (4wt%) to the Mg-rich coating results in a significant deterioration of the protective effect of the coating. However, addition of a small amount of graphene (1wt% and 2wt%) to the epoxy magnesium-based coatings can significantly improve the compactness of the coating and the adhesion force between coating and Mg alloy. Among them, the protective performance of the coating with the 2wt% graphene and 48wt% Mg powder is the best and the OCP result shows that the cathode protection period of the graphene modified Mg-rich coating is extended to 145 h. Thus, the protective effect of the Mg-rich coating on AZ91D magnesium alloy is significantly improved. The addition of graphene to the Mg-rich coating can effectively enhance the electrical contact between the metals, which is beneficial to improve the effective utilization of the pure Mg particles and reduce the corrosion rate of AZ91D substrate, and meanwhile does not change the protection mechanisms of the Mg-rich coating on AZ91D magnesium alloy. In addition, because of the unique two-dimensional (2D) structure and small size, graphene could prolong the penetration path of the aggressive solution and block the defect pores of the Mg-rich coating firmly, which improves the barrier property of the coating.