The invention relates to a fermentation method of black garlic, which comprises the following: (1) a step of low-temperature fermentation, which is to place the garlic at 2 to 8 DEG C for 4 to 6 days; (2) a step of high-temperature and high-humidity fermentation, which is to seal the garlic treated by the step (1) in a closed container, fill saturated NaCl solution at the bottom of the container and at a position where the saturated NaCl solution is not contacted with garlic, raise the temperature in the container to 70 to 80 DEG C, and keep the temperature for 7 to 15 days; and (3) a step ofnormal-temperature fermentation, which is to cool the closed container to room temperature after 7 to 15 days of high-temperature and high-humidity fermentation, keep the temperature continuously for2 to 6 days, and take out the fermented product to obtain the black garlic. When the method is used for producing the black garlic, the fermentation time is greatly shortened, all needed processes can be accomplished in 13 to 27 days, additives are not added in the fermentation period, the cost is greatly reduced and the making process is simple. And the method is suitable for industrial production.