The invention relates to a method for preparing methane-oxidizing bacteria on a large scale. The method includes the following steps: 1), putting the methane-oxidizing bacteria and inorganic salt into a reactor, and then injecting methane and oxygen into the reactor; 2), crushing the added gases into tiny bubbles by a crushing device in the reactor to enable the bubbles to be blended in liquid in the reactor and flow along the reactor internally together with the liquid, and preforming a fermentation process; 3), after the fermentation process is finished, determining completion of the fermentation process, performing initial condensation of a product in the reactor, and quickly cooling and drying the product after heating to obtain an initial product. The method has the advantages that the method mainly aims at preparation for methane-oxidizing bacteria production of large-scale reaction devices, the methane-oxidizing bacteria are cultivated by the devices such as the reactor, water solubility of the gases such as the methane is improved through measures such as bubble crushing, reaction efficiency is improved through addition of inorganic salt cultivation media, and accordingly, the method can be suitable for large-scale production application.