Nature of springback in sheet metal forming was analysed in the study, two stress-based objective functions were established to evaluate springback respectively from the stress point of view in an optimization problem aimed to reduce springback. To evaluate springback more comprehensively, multi-objective functions including a stress-based and a strain-based objective function were applied. Results show that when acting in conjunction with strain-based objective function, objective function which is defined on stress component deviation through thickness direction has perfect performance, while objective function which is defined on equivalent stress deviation through thickness direction would work well only when degree of plastic deformation is large for the stamped part. To evaluate the influence of stress position on springback, the parametric coordinate of integration point in thickness direction was also employed as weight factor for those two stress-based objective functions. Accuracy of the proposed two objective functions was also compared with the traditional objective function which is defined on the corresponding nodal distance of the shape before and after unloading.