The invention relates to the field of grab buckets, in particular to a grab bucket special for square objects. The grab bucket comprises an upper supporting beam, a rotary board, a pair of bucket valves, valve rotation hydraulic cylinders and grabbing devices, wherein the rotary board is located on the lower portion of the upper supporting beam; the bucket valves are located on the two sides of the rotary board; the valve rotation hydraulic cylinders are located between the upper supporting beam and the bucket valves; the grabbing devices are located on the inner sides of the bucket valves and comprise supporting boards, fixing parts, bolt rods, grabbing boards, grabbing hydraulic cylinders and buffering rubber; each bolt rod is divided into a first rod body on the upper portion and a second rod body on the lower portion; in the working process, the valve rotation hydraulic cylinders stretch out and draw back to drive the two bucket valves to rotate around the rotary board, the two bucket valves are opened and closed synchronously in opposite directions, and the grabbing devices can rotate on the bucket valves. The grab bucket not only can be used for grabbing cylindrical objects, but also can be used for grabbing, lifting and conveying the square objects, and is wide in application range.