Rocks are heterogeneous by nature, and the assumption of homogeneity cannot accurately explain the microscopic mechanism underlying macroscopic phenomena correctly. Digital core technology captures the geometrical structure of rocks at the microscale, providing an important tool for the quantitative characterization and multiscale study of the physical and mechanical properties of rocks. This review summarizes the process of the digital core construction method in sequence, covering imaging technology, image processing, and reconstruction. The benefits and drawbacks of the involved methods are compared. Furthermore, the application of the digital core in numerical modeling for rock mechanics is reviewed. Although extensive efforts have been made in digital core reconstruction and its application, several challenges remain to be addressed. On the basis of this review, future research will likely focus on the development of large-scale and high-precision digital cores, integrating them with advanced constitutive models, multiphysics fields, and three-dimensional (3D) printing technology to further improve their credibility.