Abstract: The graphite felt (GF) was pretreated with H₂O₂, and then Sn was electrodeposited on pretreated GF. At last, the SnO₂ modified GF was obtained by oxidation of Sn at 120℃ for 24 h. The morphologies of GF before and after modified by SnO₂ were characterized by SEM, and the electrochemical properties of GF modified by SnO₂ were investigated by cyclic voltammogram. The results show that the SnO₂ coating is uniformly formed on the surface of GF. The oxidation peak current increases from 0.053 8 A to 0.070 8 A, which means 31.5% improves before and after SnO₂ modification of GF. The duration time of oxidation enhances after SnO₂ modified, which indicates that SnO₂ performs a catalytic action upon the reaction of vanadium ions. In addition, the potential of oxygen evolution increases from 1.382 V to 1.517 V. Therefore, the electrochemical window of GF electrode in VOSO₄ solution is widened by modification of SnO₂.