In order to obtain reliable strain field , full-field strain measurement based on least-square fitting of local displacement for digital image correlation method is proposed. The principle of digital image correlation (DIC) method is introduced,and full-field strain measurement based on local least-square fitting is expatiated, strain calculation near the border, hole and crack are also discussed. The results from homogeneous deformation test and the tensile test of the aluminum specimen with a hole in the center obviously demonstrated the validity of this technique. Large strain calculating window is recommended to use in case of homogeneous deformation,so calculation results approach true value; For inhomogeneous deformation, large calculating window should be selected to according to the noise level of the local displacement field, but when displacement field has high accuracy, smaller calculating window is selected.