The invention relates to a method for detecting the chemical oxygen demand through photoelectrocatalysis by a TiO2 nanometer hole array electrode, which belongs to the technical field of environment monitoring. The photoelectrocatalysis reaction of determining COD is carried out in a reaction pool by taking a metal titanium base TiO2 nanometer hole array film as an optical anode, a metal platinumsheet as a counter electrode, an Ag/AgCi as a reference electrode and an inertia inorganic salt such as sodium sulfate as an electrolyte, adding a water sample liquid of the COD to be determined intothe reaction pool and applies a biasing voltage of 0.2 to 1.5V on the anode, illuming ultraviolet light on the optical anode of the TiO2 nanometer hole array film through a quartz window at one side of the reaction pool, and determining the COD value by determining an electrochemical signal of the organic photoelectrocatalysis reaction in the reaction pool. The optical anode adopted by the invention has the advantages of strong stress change cracking action caused by the tolerance mechanical acting force or the change of the tolerance environment temperature of a light anode, high stability and high photoelectrocatalysis efficiency; the method can improve the stability of the method for determining the water quality COD by adopting photoelectrocatalysis.