A fixing structure for safety helmet fastening strap, including a frame body mounted under a bottom of a helmet shell. The frame body has multiple fixing seats each of which is formed with a passage and an opening through which a fastening strap can pass. The fixing seat has arms extending from the fixing seat. The fixing seats are securely connected with the frame body with better load capability. Accordingly, the fixing seats can bear the extrusion force of the injection molded foam material without deflection or displacement. The helmet shell, the frame body and the fixing seats are bonded with a foam material filler to together form an integrated body. The arms of the fixing seats help the fixing seats and the frame body to hold the foam material filler.