Digital image correlation (DIC) is a non-contact, full-field optical measurement method that has been extensively used in various applications like structural health monitoring, material characterization, high temperature testing etc. However, most of the above applications are used in the laboratory, and rarely employed in the actual structure. This is mainly because of, firstly, DIC instruments are expensive and cannot be afforded by ordinary people. Secondly, the corresponding equipment is complicated to operate and cannot be widely used. The built-in camera of the smartphone is becoming more and more high-definition so that it has brought about an opportunity to solve this problem. From this point of view, this study monitored the deformation of compressive concrete blocks by smartphone and DIC technology, and analyzed the changes of displacement and strain field on the surface of concrete blocks under different loads. The location and shape of cracks in the displacement results were compared with those in the actual image as well. The results show the feasibility of using smartphones to monitor the strain of structures.