n order to reduce the cylindrical billet deformation defects in open punching process and keep its workpiece height nearly unchanged, taking the Φ60 mm×55 mm cylindrical billet as an example, the billet was punched with different aperture ratio of 2.50, 2.75 and 3.00 using the Deform3D software, and the preform billet shape was got that 9.1%3.8% increase is needed in the outside height，a convex top surface with 27.1%24.0% height compared to the corresponding punch diameter is needed in the top surface whose diameter is unchanged, 14.2%9.3% decrease is needed in the bottom surface diameter，and a waistlike side surface is obtained between the top and the bottom surface. All of the blind hole and the through hole workpieces were improved obviously in the shape accuracy when punching the preform billet (the aperture ratio is 2.50, the blind hole workpiece has a flatness of 0.6 mm and cylindricity of 0.4 mm compared to the cylindrical workpiece of 6.3 mm and 5.9 mm respectively). The results were proved by experiment，which can provide references for the practice.