The invention discloses preparation and application of an efficient and novel porous nitrogen oxide nanosheet catalyst electrode (Co3O3.62N0.38). According to the preparation of a porous Co3O3.62N0.38nanosheet catalyst, with a cheap graphite sheet as a substrate, by using an electrochemical deposition method, a Co(OH)2 precursor is prepared; then the precursor is annealed at 400 DEG C under the ammonia atmosphere for 2 hours. It is proved through DFT theoretical calculation that the porous Co3O3.62N0.38 nanosheet catalyst has good electric conductivity and excellent adsorption free energy onan intermediate, and therefore the porous Co3O3.62N0.38 nanosheet catalyst shows excellent electrochemical catalysis oxygen production performance and has ultralow overpotential of electrolytic waterand low Tafel. Meanwhile, the synthesis method of composite electrode is simple and efficient, synthesis is economical, the synthesis cost is low, and the electrode is suitable for industrial application of electrochemical water decomposition and has great scientific significance.