The steering knuckle was hard to be formed because of complex shape and high quality requirement. This paper predicted fold defect in forging based on numerical simulation. The whole process was reviewed and the cause of fold and evolution was analyzed. Further more, the effect of different fillet radius as well as draft angles on fold was compared. Accordingly, the measures were presented. Finally, the process tryout was done at site. This was quite in accord with the results of simulation. As a result, the optimum analyzed technical parameters were obtained and the fold was avoided.