A system for mooring an offshore structure group (2, 2A, 2B, 2C, 2D, 2E, 2F), wherein the system comprises: an offshore structure group including a plurality of offshore structures (10, 10A, 10B, 10C, 10D), mooring bases, and mooring lines (20, 20A, 20B) arranged respectively in three to eight directions, wherein at least one of the offshore structures (10, 10A, 10B, 10C, 10D) in the offshore structure group is moored by locking the mooring lines (20, 20A, 20B) in the respective directions with separate mooring bases, and at least one of the mooring bases locks the mooring lines (20, 20A, 20B) which are connected respectively to three to eight of the offshore structures (10, 10A, 10B, 10C, 10D) in the offshore structure group characterized in that the system (2, 2A, 2B, 2C, 2D, 2E, 2F) comprises an arrangement pattern, wherein in said arrangement pattern each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by two long mooring lines and one short mooring line included in the mooring lines (20, 20A, 20B), and mooring directions of the short mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in the same direction, or each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by two long mooring lines and one short mooring line included in the mooring lines (20, 20A, 20B), and mooring directions of the short mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in opposite directions from each other, or each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by one long mooring line and two short mooring lines included in the mooring lines (20, 20A, 20B), and mooring directions of the long mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in the same direction, or each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by one long mooring line and two short mooring lines included in the mooring lines (20, 20A, 20B), and mooring directions of the long mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in opposite directions from each other. an offshore structure group including a plurality of offshore structures (10, 10A, 10B, 10C, 10D), mooring bases, and mooring lines (20, 20A, 20B) arranged respectively in three to eight directions, wherein at least one of the offshore structures (10, 10A, 10B, 10C, 10D) in the offshore structure group is moored by locking the mooring lines (20, 20A, 20B) in the respective directions with separate mooring bases, and at least one of the mooring bases locks the mooring lines (20, 20A, 20B) which are connected respectively to three to eight of the offshore structures (10, 10A, 10B, 10C, 10D) in the offshore structure group characterized in that the system (2, 2A, 2B, 2C, 2D, 2E, 2F) comprises an arrangement pattern, wherein in said arrangement pattern each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by two long mooring lines and one short mooring line included in the mooring lines (20, 20A, 20B), and mooring directions of the short mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in the same direction, or each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by two long mooring lines and one short mooring line included in the mooring lines (20, 20A, 20B), and mooring directions of the short mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in opposite directions from each other, or each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by one long mooring line and two short mooring lines included in the mooring lines (20, 20A, 20B), and mooring directions of the long mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in the same direction, or each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by one long mooring line and two short mooring lines included in the mooring lines (20, 20A, 20B), and mooring directions of the long mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in opposite directions from each other. each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by two long mooring lines and one short mooring line included in the mooring lines (20, 20A, 20B), and mooring directions of the short mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in the same direction, or each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by two long mooring lines and one short mooring line included in the mooring lines (20, 20A, 20B), and mooring directions of the short mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in opposite directions from each other, or each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by one long mooring line and two short mooring lines included in the mooring lines (20, 20A, 20B), and mooring directions of the long mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in the same direction, or each of the offshore structures (10, 10A, 10B, 10C, 10D) is moored by one long mooring line and two short mooring lines included in the mooring lines (20, 20A, 20B), and mooring directions of the long mooring lines of each adjacent ones of the offshore structures (10, 10A, 10B, 10C, 10D) are oriented in opposite directions from each other.