The invention discloses a method for in-situ preparation of an ultra-small-size metal oxide nano catalyst material on the surface of conductive glass through electrochemical post-treatment by taking aconductive infinite coordination polymer nano material as a precursor by a one-step method. On the basis, the conductive glass element is utilized to construct a device supporting ultra-small-size composite nano catalytic material, and the loaded ultra-small-size composite nano catalytic material device is applied to dye wastewater real-time degradation monitoring and process regulation and control. The preparation method provided by the invention is simple and convenient, conditions are mild, the synthesized ultra-small-size nano material is excellent in catalytic performance, an oxidizing agent can be effectively activated, and efficient degradation of the dye is realized. Besides, a device constructed by utilizing the conductive glass supporting the nano-catalyst is good in stability and easy to assemble, and real-time monitoring of the degradation process of actual samples of different colored wastewater is realized. The method has important significance for developing online monitoring equipment and realizing evaluation and process control in the industrial wastewater treatment process, and has a good application prospect in the aspect of treating industrial dye wastewater.