The problems of phenolic resin/graphite composite bipolar plates are their brittleness and poor mechanical strength. In this study, coupling agent was used to enhance the interfacial adhesion of composite and thus improve the flexural strength. The influence of the types, treating methods and content of coupling agent on the properties of bipolar plates were investigated. Results have shown that a sharp increase of flexural strength was observed for bipolar plates prepared by graphite modification, while the conductivity decreased modestly. Meanwhile, the bipolar plates prepared by resin modification offer high conductivity and excellent flexural strength. Therefore, it can be concluded that resin modification is more suitable for the fabrication of composite bipolar plates. When 0.7wt% of the coupling agent is added to the composite by resin modification, the composite bipolar plate modified by silane coupling agent has a conductivity of 70.3 S·cm-1 and a flexural strength of 33.3 MPa. And for the composite bipolar plate modified by titanate coupling agent, the conductivity and flexural strength are 73.8 S·cm-1 and 32.1 MPa, respectively. These values well satisfy the requirements of composite bipolar plates.