Disclosed is a method to assemble a marine structure. According to an embodiment of the present invention, the method includes: a step of manufacturing a lower structure including multiple pillars vertically stood up; a step of combining a frame structure with the lower structure to support the pillars; a step of launching the lower structure combined with the frame structure; and a step of combining an upper structure with an upper part of the launched lower structure. The step of manufacturing the lower structure manufactures the lower structure while including a part of the frame structure in the lower structure.
