The invention provides a metal-air battery air electrode and a preparation method thereof. The method comprises the steps: mixing a metal organic framework material with nitrogen source micromolecules, so that the nitrogen source micromolecules are adsorbed in the metal organic framework; then, carrying out high-temperature carbonization treatment in a nitrogen atmosphere; finally, carrying out acid treatment to remove metal particles to obtain a nitrogen-doped porous carbon material; and preparing the porous carbon material into slurry, and coating the surface of a conductive substrate with the slurry to obtain the air electrode of the metal-air battery. The nitrogen-doped porous carbon prepared by the method has high specific surface area, high nitrogen content and excellent oxygen reduction catalytic activity, the PVDF binder is added into the prepared slurry to ensure the connection between the catalyst and the substrate, and the erosion of electrolyte to the catalyst is resisted through the PTFE film, so that the stability of the electrode is maintained. The preparation method provided by the invention is simple and feasible, has good repeatability, is convenient for large-scale production, and can be used in the field of air batteries, especially air electrodes of lithium air batteries.