A hook seat tightening structure for ship covers comprises a body constituted by a seat and a housing, wherein two rollers, one turntable, one wheel, one lock bolt, and one lock member are located therein. A depressing piece and a tenon are located at two sides of the lock bolt respectively. The lock bolt can be rotated and elastically restored by the tenon, which is connected with a spring. The depressing piece is pressed against one-way ratchets on the turntable, and the lock bolt can be rotated subject to a control by a key. A rope enters and is reeved on the turntable and wheel, to constitute a tightening device permitting a one-way gliding of the rope. Accordingly, when the lock member is locked by rotating the key, the tenon on the lock member can be latched on the depressing piece of the lock bolt, thereby achieving a locking function.