Abstract: Axial deformation formula of cylindrical closed-coil spring, a derived formula based on energy method of the torsional deformation in the course of mechanics of materials, is verified by a simple experimental method proposed in this paper. The axial deformation of a spring is accurately measured by using digital image correlation (DIC) method to calculate its spring constant. According to axial deformation formula of spring in the textbook of mechanics of materials, the shear modulus of spring material is calculated to prove the correctness of the axial deformation formula. The proposed test method is easy for students to practice because of its intuitive simplicity and avoidance of complicated data processing. In addition, students can have a better understanding of digital image correlation method and the theoretical formula of torsional deformation in the course of mechanics of materials. The proposed method both applies in mechanical test teaching and tests the mechanical property of a spring as well.