An integrated disassembling and assembling system for a large offshore structure, comprising a semi-submersible vessel 1, a semi-submersible vessel II, multiple lifting arms I, multiple lifting arms II, and an offshore structure, characterized in that a support I and a support II for the lifting arms I are mounted on the semi-submersible vessel I through bolts; a support I and a support II for the lifting arms II are mounted on the semi-submersible vessel II through bolts; the lifting arms I are arranged on the semi-submersible vessel I in parallel; the lifting arms II are arranged on the semi-submersible vessel II in parallel; the lifting arms I and the lifting arms II are provided with a lifting system having a three-way motion compensation function; the lifting system is provided with locking mechanisms; before lifting, the locking mechanisms is configured to lock the lifting arms I and the lifting arms II in a front-back direction and a left-right direction, and a lifting mechanism is configured to lift the offshore structure up; the lifting system having the three-way motion compensation function further comprises a mobile cart I and a mobile cart II; a bottom at a front end of each of the lifting arms I and the lifting arms II is mounted at an upper end of the mobile cart I; a rear end of each of the lifting arms I and the lifting arms II is mounted at an upper end of the mobile cart II; a lower end of the mobile cart I is mounted on the support I; a lower end of the mobile cart II is mounted on the support II; the support I and the support II are respectively fixed on the semi-submersible vessel I and the semi-submersible vessel II; and the lifting mechanism is configured for driving a lifted object to move up and down and is hinged to the front end of each of the lifting arms I and the lifting arms II; a road wheel set and a road wheel are mounted on each of the mobile cart I and the mobile cart II; the road wheel set is mounted on rails of the lifting arms I and the lifting arms II and the rails are configured for limiting up-down movement of a main arm; the road wheel is mounted on a rail of the support I or the support II; and the lifting arms I and the lifting arms II move left and right through the road wheel set, and move front and back through the road wheel; and a locking mechanism meshed with a fixing rack of each of the lifting arms I and the lifting arms II is mounted at the upper end of the mobile cart I; and a locking mechanism meshed with a fixing rack of the support I is mounted at the lower end of the mobile cart 1. a semi-submersible vessel 1, a semi-submersible vessel II, multiple lifting arms I, multiple lifting arms II, and an offshore structure, characterized in that a support I and a support II for the lifting arms I are mounted on the semi-submersible vessel I through bolts; a support I and a support II for the lifting arms II are mounted on the semi-submersible vessel II through bolts; the lifting arms I are arranged on the semi-submersible vessel I in parallel; the lifting arms II are arranged on the semi-submersible vessel II in parallel; the lifting arms I and the lifting arms II are provided with a lifting system having a three-way motion compensation function; the lifting system is provided with locking mechanisms; before lifting, the locking mechanisms is configured to lock the lifting arms I and the lifting arms II in a front-back direction and a left-right direction, and a lifting mechanism is configured to lift the offshore structure up; the lifting system having the three-way motion compensation function further comprises a mobile cart I and a mobile cart II; a bottom at a front end of each of the lifting arms I and the lifting arms II is mounted at an upper end of the mobile cart I; a rear end of each of the lifting arms I and the lifting arms II is mounted at an upper end of the mobile cart II; a lower end of the mobile cart I is mounted on the support I; a lower end of the mobile cart II is mounted on the support II; the support I and the support II are respectively fixed on the semi-submersible vessel I and the semi-submersible vessel II; and the lifting mechanism is configured for driving a lifted object to move up and down and is hinged to the front end of each of the lifting arms I and the lifting arms II; a road wheel set and a road wheel are mounted on each of the mobile cart I and the mobile cart II; the road wheel set is mounted on rails of the lifting arms I and the lifting arms II and the rails are configured for limiting up-down movement of a main arm; the road wheel is mounted on a rail of the support I or the support II; and the lifting arms I and the lifting arms II move left and right through the road wheel set, and move front and back through the road wheel; and a locking mechanism meshed with a fixing rack of each of the lifting arms I and the lifting arms II is mounted at the upper end of the mobile cart I; and a locking mechanism meshed with a fixing rack of the support I is mounted at the lower end of the mobile cart 1.