This work describes a two-step method of in situ electrodeposition and following oxidation to prepare carbon paper (CP) modified with tin dioxide (SnO2) particle as bifunctional electrode for vanadium redox flow battery. Electrodeposition technique was employed to load metal tin particle on CP, which was subsequently oxidized to tin dioxide at high temperature. CPs modified by SnO2 with different content (CP/SnO2-1, CP/SnO2-2, and CP/SnO2-3) were obtained by controlling electrodeposition time. CP/SnO2 presents an increase in electrochemical performance including faster charge and mass transfer compared with pristine CP. Among all samples, CP/SnO2-2 with proper decorated SnO2 exhibits superior electrocatalytic performances for V3+/V2+ and VO2+/VO2+ reactions. Raised performances can be attributed to that SnO2 nanoparticles provide more active sites leading to rapid electrochemical kinetic of vanadium redox reactions. In addition, mass transfer can be accelerated due to the excellent hydrophilicity of SnO2. The cell using CP/SnO2-2 as bifunctional electrode exhibits better stability and higher capacity retention during 50-cycle charge-discharge test. The cell for CP/SnO2-2 shows higher energy and voltage efficiency, suggesting that introduction of SnO2 can decrease electrochemical polarization. At 150 mA cm(-2), energy efficiency of the cell increases by 7.8% through using CP/SnO2-2.