The utility model relates to a measure technology field, and specially relates to a steel lock fastener used for a measuring instrument box. The steel lock fastener used for a measuring instrument box is characterized by comprising a fastener ring and a fastener hook. The fastener hook comprises a base plate and a hook. The fastener ring comprises a hook ring, a fastener handle, a fixing hole and a base plate; the fixing hole is positioned in the base plate; the fastener handle is provided with a slit passing through the fixing hole; the fastener handle and the base plate are provided with apertures through which a spring assembly goes, and the fastener handle is hinged to the base plate in a fixed connection manner; and the hook ring passes through the aperture at the side surface of the fastener handle to be hinged to the fastener handle. The spring assembly tightly presses the hook ring to guarantee stability, the wear resistance is good, usage is convenient, installation is fast, and the replaceability is high.