A sub-frame for a dump truck comprises an integral cross beam and longitudinal beams. A cylinder support and a main cross beam are fixed between two parallel longitudinal beams, and the longitudinal beams are welded with the integral cross beam of the integral communicated structure. The two ends of the integral cross beam are provided with structure which is connected with a roll-over seat. An inclined support is used for fastening the integral cross beam and the cylinder support. The sub-frame is distributed symmetrically along the center line. Compared with a tri-detached sub-frame, the invention has the advantages of simple process, stronger intensity, saving raw materials, reasonable structure and larger stability.