The invention discloses a preparation method of a solid microbial inoculant. The method comprises the following steps: concentrating a strain culture solution, adding an inhibitor, uniformly mixing a certain amount of solid adsorbing carrier, drying the mixture, and adding a deoxidizer to obtain the solid microbial inoculant. The method can enhance the storage time and viability of the solid microbial inoculant and lower the preservation and transportation cost; and the inhibitor and iron powder deoxidizer are added to lower the microbiological contamination probability, prevent the residual organic matters of the strain culture medium from oxidation, lower the activity of the target strain to some extent and perform promotion functions on prolonging the storage time.