Redox flow batteries (RFBs), regarded as the most effective grid-scale electrochemical energy storage technology, are attracting wide attention because of the problems of the energy crisis and environmental pollution. Charge transport properties are critical factors related to the electrochemical performance of energy storage devices. Nanocarbons, which have special morphologies and many physicochemical properties, such as high ionic conductivity, high thermal conductivity and excellent mechanical properties, can play an indispensable role in electrochemical energy storage. Adjusting the microstructure of carbon materials is an effective strategy to improve their electron and ion transport behavior. In this work, the functions of nanocarbons in RFBs are reviewed, especially focusing on the modification and design of nanocarbons used in the electrodes, suspended electrodes in semi-solid RFBs, and bipolar plates (collectors) used to improve the energy efficiency, power density and the stability of high-performance RFBs. A more systematic and comprehensive understanding of the role that nanocarbons play in RFBs could provide a new perspective for the design of high-performance RFB electrodes.