Optimzation methods are applied to sheet metal hemming. For the determination of parameters that influence the roll-in, an approximation Hemming model is proposed, to be used with optimization methods. The small area of sheet metal hemming lead to low efficiency, while the approximation hemming model can solve the problem, which make hemming model optimization possible. And the approximation hemming model based certain optimization method offer a new method to control the roll-in in hemming.