Accurate characterization of contact deformation is of great difficulty especially for the area close to the interface. In this work, a theory-aided strain measurement method by combining modeling and experimental identification is developed for the characterization of contact deformation. The method consists of three procedures including displacement measurement, mechanical modeling, and strain identification. The displacement measurement introduces a modified digital image correlation to acquire the displacement field. In mechanical modeling, a contact model is developed so the relationship between the interfacial stress and the displacement is formulated. Finally, the strain identification procedure is used to optimize the unknown parameters by matching the modeled displacement to the experimental data, and then reconstruct the strain field using the model and the optimal parameters. By developing a discrete interfacial stress model and strain reconstruction algorithm, the proposed method can sensitively identify the strain concentration in the contact vicinity. Both simulation and experiment are carried out, and the effectiveness of the proposed method is discussed in detail.