The invention belongs to the technical field of chain-grate machine equipment in metallurgy industry and particularly relates to a tensioning mechanism of a chain-grate machine, which comprises a tensioning frame, a tensioning wheel sliding support and a tensioning wheel. The tensioning wheel sliding support is connected with a movable block support; a movable block is arranged on the movable block support; both the movable block and a fixed block are meshed and connected with a steel wire rope; and the two ends of the steel wire rope are connected with a winch and a tensioning control device. The tensioning control device consists of a pull rod, a spring right spacer sleeve, a spring, a spring left spacer sleeve, a fixed sleeve, a hinged shoe and a tensioning regulation device. The tensioning regulation device consists of a sliding rod support, a sliding rod, a sensing sliding block, three sensors and a bracket and a dust cover. The mechanism has the advantages that: the stepless andcontinuous automatic regulation of tension of a grate bed can be realized; the regulation is timely, accurate and reliable; and the tension of the grate bed is kept within a preset value range constantly, labor force is saved, and the high-efficiency production of the chain-grate machine is guaranteed.