The invention relates to a preparation method of a 5-mercapto-1H-tetrazole compound shown in a formula (III), which comprises the following steps of: (1) dissolving disulfide in halogenated alkane, dropwise adding a chlorinating reagent at -5 to 0 DEG C, carrying out heat preservation reaction for 2-5 hours, and carrying out reduced pressure distillation at 5-10 DEG C to obtain chlorinated disulfide; (2) dissolving the chlorinated disulfide prepared in the step (1) in lower saturated monohydric alcohol, dissolving sodium azide in water, dripping a sodium azide solution at 20-30 DEG C, heatingto 50-65 DEG C after dripping, and carrying out heat preservation reaction for 2-5 hours; (3) evaporating the solution obtained in the step (2) at 40-45 DEG C under reduced pressure to remove the lower saturated monohydric alcohol, and adding halogenated alkane for extraction for three times to obtain a halogenated alkane extraction liquid; (4) concentrating and crystallizing the halogenated alkane extraction liquid prepared in the step (3), and filtering to obtain the 5-mercapto-1H-tetrazole compound. The preparation method has high yield, good product quality, convenient solvent recycling and low production cost.