Abstract: The embodiments of the present application, belonging to the technical field of medical test and assay, and provide a preservative for an in vitro diagnostic reagent. The preservative includes a combination of a sulfadoxine solution and a dimethoprim solution, wherein a molar ratio of sulfadoxine in the sulfadoxine solution to dimethoprim in the dimethoprim solution is from 0.002 to 1. The present disclosure also provides use of the preservative for the in vitro diagnostic reagent. The technical solutions according to the embodiments of the present disclosure improve stability of the reagent, do not affect reactions of the reagent, and may be extensively applied.