The utility model relates to the technical field of installation of reinforcement cages for bored pile construction, in particular to a reinforcement cage positioning fixture with diameter-adjustablescale marks. The device comprises an upper steel belt ring and a lower steel belt ring, each of the upper steel belt ring and the lower steel belt ring is correspondingly provided with at least one opening; the end parts of the upper steel belt ring and the lower steel belt ring at the opening are respectively laminated together; at least one bolt penetrates through the outer side end of the uppersteel belt ring and the outer side end of the lower steel belt ring at the overlying position from outside to inside, sliding holes which are correspondingly matched with the bolts in a sliding and fastening mode are correspondingly formed in the inner side end of the upper steel belt ring and the inner side end of the lower steel belt ring at the overlying position, and scales are marked on thecircumferential edges of the sliding holes. The fixture ensures that the reinforcement cage is centered and the thickness of a protective layer meets the design requirements. According to the utilitymodel, when the bored pile reinforcement cage is mounted, the reinforcement cage is not centered, and the protection layer is controlled integrally, so that the problems that the reinforcement cage isnot centered and the protection layer is difficult to control accurately in a large-area construction process are solved, and the bored pile construction quality is ensured.