The invention relates to a preparation method of a biochar bacterium fertilizer. The method comprises the following steps: 1, preparing biochar: carbonizing a raw material under anaerobic conditions, and respectively storing the produced biochar and wood vinegar for later use; 2, preparing carbon a decomposition enzyme and a bacterial community: embedding a medium in soil for the spring, summer and autumn to obtain the carbon decomposition enzyme and the bacterial community, and carrying out group expansion breeding on the obtained carbon decomposition enzyme and the bacterial community to obtain the carbon decomposition enzyme and a biological bacterium dry carrier; and 3, preparing the biochar bacterium fertilizer: crushing 100 parts by weight of the biochar, adding 10-30 parts by weight of the carbon decomposition enzyme and the biological bacterium dry carrier and 5-10 parts of the wood vinegar, adding water until the water content is 50-60%, carrying out anaerobic fermentation for 10-30d to decompose stable elemental carbon in the biochar into 10-50% of water-soluble effective carbon, sieving the prepared fertilizer particles by 8-10 mesh sieve, taking the obtained oversize product, and packaging to obtain the biochar bacterium fertilizer. The water-soluble effective carbon content of the biochar bacterium fertilizer is 5-10 times that of a common organic fertilizer, the biochar bacterium fertilizer combines slow release and quick action, and the fertilizer effect of the biochar bacterium fertilizer is 3-5 times that of the common organic fertilizer.