The invention provides a photoelectrical FenDun method for removing the non-degradable organic substance in water, which combines photochemistry reaction and electrical FenDun reaction to co-treat the organic substance effectively with multiple actions. The invention also provides a device applying the photoelectrical FenDUN reaction to remove organic substance in water, which comprises: the reactor employing shape stable electrode (DSA) as anode, employing activated charcoal as cathode, putting the low pressure mercury vapor lamp closed in the quartz glass tube vertically between the anode and cathode and venting a certain quantity of oxygen to the cathode surface, adding marginal ferrous salt into the organic wastewater with pH being about 3 as catalyst and importing current flow for electrolysis to remove pollutant. The invention oxides and degrades organic substance by using the hydroxyl free radical generated by photochemical reaction and electrical FenDun reaction, the hydroxyl free radical possesses strong oxidability which can oxide organic substance without selection, and is characterized by the complete, fast and effective oxidation and no secondary pollution.