Abstract: Expansion drawing process without external die for large-diameter thin-walled cupronickel pipes from Φ273×16 mm to Φ330×11 mm was simulated by Deform-3D. Evolution of the circumferential stress and changing regularity of the pipe size during the drawing process were analyzed. The results showed that in the process of drawing without external die, the circumferential stress of the expanding part moved from tensile stress on the outer surface to compressive stress on the inner surface, and the circumferential stress of the rebound part moved from compressive stress on the outer surface to tensile stress on the inner surface. With the increase in the pipe diameter and decrease in the wall thickness, the circumferential stress distribution on the inner and outer surfaces of the pipes was more concentrated. Obvious rebound appeared in the pipes after expansion. Related to the thickness of original wall and the ratio of expansion, the correlation model S=16.0986+0.9256×S₀-14.8743×D/d(mm)could predict the wall thickness of the expanded pipes well.