The traditional steel sea anchor cannot provide enough traction force when large cutter suction dredger is excavating hard soil,so the excavating force of cutter cannot be exerted.We provide a variable load gravity box anchor to replace the traditional steel sea anchor,and analyze the strucure and characteristic of variable load gravity anchor by the example of the large cutter suction dredger “Tianjing”.The size of box anchor is based on the soil quality,sea condition and the pressure to ground.The amount of ballast iron can be changed according to the need.The pressure to the ground can be generated by the gravity of the anchor itself to provide enough grip force,and provide enough transverse pulling force for large cutter suction dredger.The productivity of large cutter suction dredger can be greatly improved.