The invention discloses a direct-vat-set fruit vinegar leavening agent produced by taking millet as a raw material and utilizing a solid state method, and a preparation method of the fruit vinegar leavening agent. Raw materials of the fruit vinegar leavening agent comprise acetobacter pasteurianus and a solid medium. The method comprises the steps of cultivating acetic acid bacteria seeds by taking glucose, beef extract and the like as raw materials, inoculating the prepared microorganism seeds into a millet culture medium, performing solid fermentation under a certain cultivation condition, freeze-drying the prepared culture in a drying box of a freeze-drying machine, removing the excessive water and performing sterile crushing to obtain the direct-vat-set fruit vinegar leavening agent. The millet can serve as a nutrient in the solid state culture process and also can serve as a substrate for microorganism growth, the undecomposed starch in the miellet can serve as a freeze-drying protective agent to reduce or prevent damage to cells caused by freeze drying or rehydration, the original physiological-biochemical characteristics and biological activity are maintained as much as possible, and the freeze-drying protective agent does not need to be added additionally, so the operation procedure is simplified and the cost is saved.