The utility model relates to a measure technology field, and specially relates to an automatic spring fastener used for a measuring instrument box. The specific scheme is provided as following: the spring fastener comprises a straight rod fastener and a slot fastener; two sides of the straight rod fastener and two sides of the slot fastener are provided with bayonets correspondingly matched to the measuring instrument box; the straight rod fastener comprises a cuboid fastener block and two guiding straight rods below the cuboid fastener block, and the tail end of each guiding straight rod is provided with a block tooth directed outwards and a groove locking port at the inner side; and the slot fastener possesses two slots corresponding to the guiding straight rod, two sides of the slot fastener possess two buttons and locking port assemblies arranged in the slot fasteners, each locking port assembly is extended to the inner side of the corresponding slot, and each locking port assembly is encircled by a spring assembly and is corresponding to the groove locking port of the corresponding guiding straight rod. The automatic spring fastener provides the advantages as following: the fastener structure is supported by the spring assembly, the locking performance is excellent, the automatic spring fastener is wear resistant, usage is convenient, installation is fast, and the replaceability is high.