The invention belongs to the technical field of spinning forming, and discloses a multi-pass spinning forming method for a long barrel with inner annular reinforcing ribs. An inner spinning technologyand a tension spinning technology are combined, only a set of annular core dies with different inner diameter sizes and the length being 400 mm are adopted to achieve multi-die multi-pass spinning forming of the long barrel part with the multiple inner annular reinforcing ribs and the length being 2m or less, and the part reinforcing rib position and size precision can be ensured. The method comprises the steps of spinning workblank design, spinning workblank machining, stress relief treatment, workblank installation adjusting, multi-pass spinning, turning, stress relief treatment and the like. Multi-pass low-cost forming of the long barrel with the inner annular reinforcing ribs is achieved, and the material utilization rate is greatly improved; and compared with a traditional technology, the technological risk and the difficulty of multi-pass accurate forming of the inner annular reinforcing ribs are lowered, the material cost is reduced, and the product quality is improved.