The invention discloses a quick-assembled combined mandrel. The quick-assembled combined mandrel comprises a base; the outer circle of a molded line mandrel is assembled and connected with an inner hole in one end of the base; the base is fixed through an axial adjusting jackscrew, a radial adjusting jackscrew and a locking bolt; a workpiece is put in a molded line groove formed by the end surfaces of the molded line mandrel, and the two are pressed through a pressing pad; and a pressing bolt penetrates through a step hole in middle of the pressing pad to fix the pressing pad and the base. The quick-assembled combined mandrel can quickly replace different molded line mandrels according to molded line characteristics of various parts, can align the end jump and the diameter jump of the mandrels through simple adjustment to achieve self-turning effect on a lathe, and improves the production efficiency; and meanwhile, various molded line mandrels can be recycled to save the resource consumption.