Water splitting is deemed as an effective pathway for producing ideal clean energy, such as hydrogen. Here, a copper oxide film (Cu-Tris film) was prepared in-situ from a 0.2M phosphate buffer solution (pH=12.0) containing 1.0mM Cu2+ and 2.0mM Tris via controlled-potential electrodeposition. The Cu-Tris film showed a significantly low overpotential of 390mV at a current density of 1.0mA/cm2 for electrocatalytic water oxidation. Simultaneously, a considerably low Tafel slope of 41mV/decade was achieved. This Cu-Tris film also exhibited a high and stable current density of ca. 7.5mA/cm2 at 1.15V vs. NHE for long-term electrocatalysis (10h). These results demonstrated the superior performance of the developed Cu-Tris film, which should be attributed to the regulating effect of the five coordinated planar structure of the Cu-Tris complex precursor during the process of electrodeposition.