Iron black cathode is a new electrode material for cathode in the industry of chlorate electrolysis. Its structure and composition are examined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The overpotentials of hydrogen evolution on the iron black cathode in the electrolyte of chlorate electrolysis decrease by 260-270mV(65±2℃) in comparison with the original iron cathode. During 90 days of life test hydrogen overpotentials of iron black cathode are lower than that of original iron cathode by over 240 mV under the conditions of current density 2kA/m2 and temperature 65±3℃.