The XPS results show that there are O, Oil and 112O on the surface of RuO2 electrode. Their Ols Peaks locate at binding energies 529.5, 531.0 and 532.0 (533, 3)eV, respectively. It has been found that graphite carbon exists in the RuO2 electrode, It is suggested that oxygen is evolved by the decomposition of RuO4 which is the oxidized Product of Ru2O3.