A height adjustment mechanism for a headrest includes: a locking member configured to be locked with a height adjustment gear, the locking member having a first locking position and a first unlocking position, and the locking member being capable of switching between the first locking position and the first unlocking position; an operating member having an initial position, a first operating position and a second operating position; a safety lock structure configured to lock the locking member in the first locking position, the safety lock structure being movably connected on the operating member; and a driving member, one side of the driving member being slidably connected to the operating member, the other side of the driving member abutting against the locking member.