Abstract: Web thickness is one of the important parameters in Closed-die forging process,which has an effect on forming force of die forging and material consumption.In this paper,the optimum design of web thickness is done by Upper Bound Element Technique(UBET),Based on the relation of the web thickness and the flash height,three kinds of deformation flow models and kinematically admissible velocity fields are established,and the optimum upper-bound solution of maximum forging force identical with the experimental result is obtained by Upper Bound Theory,Golden section method and programme compiled using Turbo C language.It is shown that the kinematically admissible velocity field designed is reasonable.Taken the product of maximum forging force and web volume as an optimigation rule,the optimum web thickness can be obtained.