The present invention relates to the field of lawn mower equipment, in particular to a height adjustment device for a lawn mower, including connectors, screw assemblies, hollow columns, hinges, movable rods, spring tubes, decks, roller assemblies, cross bars, pillars, Ribs, limit blocks, position adjustment springs, bases, bearings, connecting rods, collars, fastening screws and lawn mower rods, screw components are arranged on the connecting parts, hollow columns are arranged at the bottom of the connecting parts, hollow columns There is an opening on the top, and a fixed plate is arranged on the top of the opening. The fixed plate is hinged with the hollow column through a hinge. The fixed plate is provided with a triangular block, and the movable rod is inserted into the hollow column. Replacement and maintenance, its adjustment function can be applied to a variety of terrains, the adjustment of the mowing height saves time and effort, and has multiple shock absorption effects, which well protects the integrity of the device and the mower bar, and prolongs the service life , has strong practicality.