Abstract: Although cross-sectional warping and compression between longitudinal fibers can cause significant errors in the beam bending normal stress calculation under transverse bending, these errors become negligible when the span-to-depth ratio of the beam exceeds 5. One of the key challenges in teaching mechanics of materials is helping students understand these specific characteristics of transverse bending. The digital image correlation (DIC) is an advanced optical deformation measurement technique that provides benefits like non-contact, full-field measurement, and simple operation. This paper explores teaching reform in three-point bending experiments by introducing the DIC method to achieve visual measurement and presentation of the deformation characteristics under transverse bending. By combining the strain field of beams with different span-to-depth ratios and generalized Hooke's law, the normal stress distribution along the cross-section height can be obtained, enabling a more comprehensive understanding of the beam bending normal stress formula. The practice shows that introducing advanced optical measurement methods to visualize key content enhances students' understanding of various related knowledge, cultivates integrative and practical skills, and stimulates their interest in scientific and technological innovation.