The invention relates to the improvement of the structure of a grab bucket mechanism achieving horizontal fishing, and provides a grab bucket mechanism which is low in failure rate and achieves horizontal fishing through a pure mechanical structure. The grab bucket mechanism is characterized in that an air cylinder is arranged on a moving rack; a special-shaped plate is arranged on a control rack; one end of the special-shaped plate is hinged to a piston rod of the air cylinder; the other end of the special-shaped plate is provided with a second connecting rod in a hinged manner; a supporting arm is arranged at the position, corresponding to the lower end of the special-shaped plate, of the moving rack; a compensation connecting rod is arranged between the supporting arm and the lower end of the special-shaped plate in a hinged manner; the middle of the special-shaped plate is connected with the control rack through a first rotary shaft; the lower end of the second connecting rod is provided with two third connecting rods in a hinged manner; the lower ends of the two third connecting rods are hinged to the ends of two open bucket connecting rods correspondingly; the other ends of the two open bucket connecting rods are connected with second rotary shafts on the two sides of the bottom of the control rack correspondingly; and corresponding buckets are arranged on the lower sides of the two open bucket connecting rods correspondingly.