The invention provides a forming method for small-radius bent pipes. A one-mold multi-piece mode is adopted. The forming method comprises the steps that the one-mold multi-piece number is analyzed and determined through a computer aided engineering tool; raw material pipes are provided and placed in a forming mold, pre-forming is conducted on the pipes, the round cross section of each pipe is made to become an oval cross section with flat upper and lower portions and wide left and right portions, and oval pipes are formed; the oval pipes are bent in a perfusion bending mode to be in a shape similar to the shape of a product; and the bent pipes are formed to be in a required shape by applying internal high pressure. According to the forming method for the small-radius bent pipes, the small-radius bent pipes with the pipe diameter being smaller than 1 D can be formed stably and reliably, and in addition, the defects that the inner side of each bent pipe is crumpled, sunken and the like due to the fact that the radius of each small-radius bent pipe is too small can be effectively overcome.