The present invention relates to a slot type fermentation method. The method comprises the following steps: (1) building a fermentation tank with a brick-concrete structure under the ground or on the ground; (2) hardening the fermentation tank bottom with concrete, uniformly arranging 1-3 ventilation channels, and arranging steps, with width of 10-15cm and 5cm from the fermentation tank bottom, on two long edges of the ventilation channels; (3) setting up a supporting permeable plate on the steps to cover the ventilation channels; and (4) uniformly piling materials to be fermented in the fermentation tank to start the fermentation. By adopting the method of the invention, the fermentation tank bottom is overhead, and does not need forced ventilation, so as to greatly save equipment investment, energy consumption, and production cost of organic fertilizer, as well as reduce the ammonia escape and odor volatilization; besides, by adopting the support permeable plate, excessive moisture in the material to be treated can also permeate to the fermentation tank bottom through the permeable plate to facilitate fermentation.