A new route to synthesize polyaniline (PANI)-grafted carboxyl-functionalized graphene (PGCG) composite material is established. In this paper, PGCG is first prepared through a two-step carboxyl-functionalized process. PANI can be grafted and grown on the surface of graphene due to the covalent bonding existing between the carboxyl-functionalized graphene and polyaniline. This method cannot only improve the mechanical performance and adaptive performance of polyaniline effectively, but also reduce the production costs and environmental pollution during the synthetic process. Therefore, a green and industrial synthetic process is achieved. X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared (FTIR) all confirm that composite materials have been prepared successfully. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicate that the as-prepared PGCG has regular structure. Thermogravimetric analysis (TGA) indicates that the addition of graphene nanosheets can significantly improve the thermostability of PANI. Moreover, the as-prepared material exhibits superior electrochemical performance. As an electrode material for supercapacitors, PGCG possesses high specific capacitance of 158 F g⁻¹ at a scan rate of 25 mV s⁻¹ and 147 F g⁻¹ at 50 mV s⁻¹ in 1 M H₂SO₄. The Nyquist plot also confirms that the PGCG has low charge transfer resistance and good capacitive behavior. These great properties make PGCG a novel electrode material with potential applications in high-performance energy storage devices.