In this study, graphene/Co3O4 composites are prepared through a simple process under mild hydrothermal conditions. Sodium carbonate (Na2CO3) can produce many OH− and CO3 2− ions after dissolution and hydrolysis in a water–isopropanol system, thereby making it applicable as both depositing agent and reducing agent in the synthesis of graphene/Co2(OH)2CO3 composites. Remarkably, the galvanosta charge–discharge test shows that the specific capacitance value of the as-obtained composites reaches a high value of 443Fg−1 at a high current density of 5Ag−1, which is significantly improved in relation to Co3O4, and the capacitance retains 54% of capacitance at 60Ag−1. The fact that the specific capacitance remains 97.1% after 1000 continuous charge–discharge cycles at 10Ag−1 indicates that the as-prepared material has an excellent cycle life. The effect of the feeding ratios between Co3O4 and graphite oxide on the electrochemical performance has also been studied.