Abstract: A seat height adjustment device includes a clutch mechanism (100) and a brake mechanism (500) which are coaxially arranged. The brake mechanism includes a bracket (8), and the bracket has a plurality of fastening components (9) that can be separately fixed corresponding to each of the mounting holes and cannot rotate with respect to the bracket (8). Each fastening component has a connecting end (91) connected to the bracket. The clutch mechanism includes a cover (1) having an outer diameter enlarged with respect to each of the connecting ends. The cover is combined corresponding with the bracket and partially or completely obscuring the connecting ends. Thereby the structure strength of the seat height adjusting device can be enhanced, and the seat height adjusting device can be installed and fixed to the seat in a general manner.