An asymmetrical structure for an open-end wrench is disclosed. The force-applying surface of the wrench facing the opening is mainly set as an arc surface, and the force-receiving surface of the wrench facing the opening is set as a flat surface. When a nut is engaged in the opening of the wrench, one side of the nut abuts against the force-receiving surface, and the other side is in contact with the force-applying point on the arc surface of the force-applying surface. When the wrench is turned, the force of the torque can only be transmitted through the force point contacting the nut, thereby preventing the force of the torque from being dispersed.