The invention provides a topside beam. The topside beam comprises: an upper topside beam that is comprised of an upper web beam (10), an upper left wing beam (12) and upper right wing beam (11), wherein the section of the upper web beam (10) has a shape of an inverted “L”; the upper left wing beam (12) and the upper right wing beam (11) are oppositely connected to the two sides adjacent to the lower end of the upper web beam (10) respectively; the upper left wing beam (12) opposite to the upper web beam (10) inclines downwardly; and the upper right wing beam (11) is located at 90° with the upper web beam. And a lower topside beam that is comprised of a lower web beam (20) and a lower right wing beam (21), wherein the lower right wing beam (21) is connected to the right side adjacent to the upper end of the lower web beam (20); and the lower right wing beam (21) opposite to the lower web beam (20) inclines upwardly and is parallel to the upper left wing beam (12). And besides, the upper left wing beam (12) and the lower right wing beam (21) are tightly connected by a connecting member.