The invention discloses a rack structure of a large-tonnage beam-erecting crane and belongs to the field of cranes. The rack structure is characterized by comprising two side trusses and two middle trusses, wherein the lower ends of the side trusses and the middle trusses are fixed on a front cross beam; the upper ends of the side trusses and the middle trusses are connected through a truss connecting cross beam; the two side trusses are arranged at the left and right ends of the front cross beam separately; the two middle trusses are arranged in the middle of the front cross beam; and a single side truss, a single middle truss, the truss connecting cross beam and the front cross beam constitute a frame taking the shape of a square. All points of the crane rack are uniformly stressed, so that the stressed capacity of the crane rack is effectively improved on the premise of keeping a simple structure, and the problem that the rack cannot be supported because the large-tonnage beam-erecting crane is large in load is solved.