Abstract: Based on the very basic assumption in image motion estimation, i.e. the gray-lever invariant assumption, the global optimization solving model for digital speckle correlation method (DSCM), which is also named as digital image correlation(DIC) method was constructed by matching the whole speckle images, instead of subsets of speckled images. Then two kinds of solving schemes for DSCM, subset matching and FEM based DSCM, could be deduced from the global optimization solving model proposed in this paper. It is emphasized that the displacement representation mode is the key to DSCM solving, so different displacement representation modes could induce different DSCM solving schemes.