Abstract: On the basis of conformal mapping, a three-dimensional metal forming problem during irregular extrusion is transformed into a two-dimensional axisymmetric problem. The normal convergence approach and the trigonometric iterative interpolation between odd and even grid points are employed in the transform. An analytical expression of the curved surface of extruding die cavity is obtained. The plastic flow during metal forming and the strain rate are given explicitly. With the help of energy principle for metal forming, the parameters for optimization of die cavity are determined. It is believed that the present work offers useful information for quick and accurate CAD/CAM integration.