The invention discloses a special-shaped flat pipe forming process. A raw material is subjected to hot extrusion, and a straight round pipe is obtained; the straight round pipe is subjected to first artificial aging treatment with the temperature being 150-260 DEG C for 2.4-3.5 hours; the straight round pipe is forged into a taper pipe; the wall face of the taper pipe is cut, and compensation quantity is reserved on the outer wall of the taper pipe; the taper pipe is subjected to solution treatment with the temperature being 480-580 DEG C for 0.8-1.4 hours; one end of the taper pipe is flatlypressed and formed; the taper pipe is subjected to second artificial aging treatment with the temperature being 200-280 DEG C for 2.4-3.5 hours; the compensation quantity on the taper pipe is cut, anda special-shaped flat pipe is obtained. A hot treatment method is adopted, the hardness of a workpiece is switched multiple times in the machining process, various types of cold machining are feasible, and influences of elastic deformation are eliminated; and a material compensation method is adopted to guaranteed that the deformation tendency at different positions on the workpiece can be withina controlled ranged in the cold machining process, the size of the workpiece is controlled, and the forming quality of the special-shaped flat pipe is guaranteed.