Digital image correlation method is widely studied and applied due to its advantages, such as non-contact, whole measurement, and simple structure. The traditional calculation method of strain fields takes the local least squares fitting process of the displacement field as the core, and uses the unified subset size of the whole field to be calculated. However, there is a biggish algorithm error in the process of heterogeneous deformation measurement. Larger strain subset size will smooth local deformation gradient, while smaller strain subset size cannot effectively reduce the displacement field error. Therefore, according to the local gradient intensity of the displacement field, a novel algorithm is proposed to correct displacement fields and dynamic select the strain for calculating the subset size, and simulate the results of the speckle images. The results show that the proposed method effectively reduces the calculation error of the digital image correlation method in heterogeneous deformation, and while the system precision is improved. The dynamic subset selection algorithm based on the local gradient intensity of the displacement fields has a simple principle and high calculation accuracy.