The invention relates to the field of electrode materials for all-vanadium redox flow batteries (VRB), particularly relates to a preparation method of a high-performance nitrogen-doped graphene modified carbon felt suitable for a full-vanadium redox flow battery, and solves the problems that a commercial carbon felt for a vanadium battery at the present stage is poor in electrode conductivity, small in specific surface area, low in electrochemical activity, poor in vanadium ion electric catalytic performance, low in single-battery performance, high in cost and the like. According to the method, a commercial carbon felt is used as a raw material, and the nitrogen-doped graphene modified carbon felt is prepared by chemical vapor deposition (CVD). The prepared composite carbon felt has high electrical conductivity, large specific surface area, high electrochemical catalytic performance, excellent chemical stability, high VRB battery performance, low cost and the like. The preparation method disclosed by the invention has the advantages of simplicity and feasibility in operation, low product cost, easiness in industrial production, environmental friendliness and the like, and can be widely applied to the field of the all-vanadium redox flow batteries.