The utility model provides a cube oil cylinder, a sealing ring and a sealing structure, wherein the sealing ring and the sealing structure are used in the cube oil cylinder. The cubic oil cylinder comprises a cylinder body with a square section, a piston, a piston rod and a sealing structure arranged between the piston and the cylinder body. The sealing structure comprises a first sealing bag ringand a second sealing bag ring arranged at the upper and lower parts of the piston; the third sealing bag ring is arranged at an opening of the cylinder body; annular sealing grooves are correspondingly formed in the outer wall of the piston and the opening of the cylinder body; the sealing bag rings are embedded into the corresponding annular sealing grooves respectively and make contact with theinner walls of the grooves, the inner groove face of each sealing groove is communicated with the oil cylinder body, and when hydraulic oil is injected in a pressurized mode, the hydraulic oil is injected into the inner groove faces of the sealing grooves to apply pressure to the corresponding sealing bag rings, so that the pistons and the cylinder body are sealed. The square oil cylinder is reliable in sealing mode, the problems that a sealing piece is uneven in contact pressure and prone to being damaged and the square oil cylinder is prone to being sealed are solved, and the square oil cylinder can replace a cylinder oil cylinder to be used in specific occasions.