In this paper, aqueous solution of reduced graphene oxide has been prepared assisted by the graphene quantum dot, which is then mixed with aqueous polyaniline solution to form water-borne reduced graphene oxide/polyaniline composite powder. The resultant graphene quantum dot-reduced graphene oxide/polyaniline shows a specific morphology of nanosized polyaniline firmly attached on reduced graphene oxide layer, due to the good dispersion of reduced graphene oxide and polyaniline in water. The monodispersion leads to the close contact between reduced graphene oxide sheets and polyaniline particles, significantly depressing the accumulation. It leads to the enhanced conductivity, supercapacitance and cycling stability for graphene quantum dot-reduced graphene oxide/polyaniline, with capacitance as high as 648 F g−1. After 5000 charge-discharge cycles, the capacitance of as-prepared reduced graphene oxide/polyaniline composite shows just 3.7% decay while it reaches 68% for polyaniline. Furthermore, driven by the strong electrostatic forces between the electropositive polyaniline and the electronegative graphene quantum dot-reduced graphene oxide as well as the π−π interactions, the obtained nanosized graphene quantum dot-reduced graphene oxide/polyaniline films from the controllable layer-by-layer method show the morphology of interconnected-layer networks and exhibit good electrochemical activity on H2O2 in the range of 5.0 × 10−7–3.5 × 10−5 M. The detection limit is as low as 1.1 μM.