Digital image correlation method is developed to determinate the plastic deformation of metal specimens. In order to detect placstic deformation, a new intensity correlation coefficient with a weighting factor is proposed. This method, firstly, determines the location of the measured points after deformation by digital image correlation, and then calculates the new intensity correlation coefficient which is used to determine whether the measured points into plastic deformation stage. The technique is proved by experiments which contain complete specimens and notched specimens. The results show that the method can accurately determine the elastic-plastic boundary of the complete specimens, and can intuitively identify the plastic region of the notched specimens.