The present invention relates to a bisulfate of a Janus kinase (JAK) inhibitor and a preparation method therefor. More specifically, the present invention relates to a (3aR,5s,6aS)-N-(3-methoxyl-1,2,4-thiadiazole-5-group)-5-(methyl (7H-pyrrolo[2,3-d]pyrimidine-4-group) amino)hexahydrocyclopenta[c]pyrrole-2(1H)-formamide bisulfate shown in the formula (I), a preparation method therefor, and an application thereof. The bisulfate shown in the formula (I) can be well used as Janus kinase (JAK) inhibitor in clinic work, so as to treat rheumatic or rheumatoid arthritis.
