The incidence of ACL injuries in the United States is 38/100,000 per year in the general population, 600/100,000 per year in soccer and 700/100,000 per year in skiing. The incidence of ACL injuries among professional athletes in China is 0.71% for women and 0.29% for men, 2.37 times higher than for men. 78% of ACL injuries occur in non-contact sports, often during landing, stopping, twisting or shearing movements. ACL injuries are usually combined with medial collateral ligament and medial meniscus injuries. In severe ACL injuries, the ligament cannot repair itself, and reconstructive surgery is usually used to restore ACL function. With further understanding of the anatomical and biomechanical characteristics of ACL, improved graft selection and management, and improved ligament fixation techniques, the results of reconstructive surgery have been improved. Clinical practice proves that the short-term results after reconstruction are good, but still 20%-25% of the reconstructive surgery has poor results, leading to re-injury of the ligament. The root cause is the lack of understanding of the normal functional anatomy and biomechanical characteristics of ACL. To further improve the therapeutic effect of ACL, it is necessary to deepen the understanding of the normal anatomy and biomechanics of ACL, to provide a theoretical basis for the study of ligament injury and repair mechanisms, to improve reconstruction techniques and to guide rehabilitation exercises. In this context, a trend is emerging–the evolution of ACL reconstruction from single-bundle reconstruction to double-bundle reconstruction. The anatomical and biomechanical characteristics of the ACL: 1. The ACL starts from the posterior part of the medial aspect of the femoral epicondyle and is attached to the anterior part of the intercondylar spine of the tibial plateau anteriorly, distally, and inwardly through the joint cavity. 2, According to the different distribution of ACL stop fibers and the difference of ligament tension during flexion and extension, the ACL is roughly divided into anterior internal bundle (AMB) and posterior external bundle (PLB). The anterior medial bundle (AMB) has two stops located in the posterior superior part of the femoral stop and the anterior medial part of the tibial stop; the posterior external bundle (PLB) has two stops located in the anterior inferior part of the femoral stop and the posterior external part of the tibial stop. Biomechanical characteristics of ACL: 1. ACL has multiple effects of limiting tibial anterior translation, internal rotation, internal and external rotation and hyperextension. The anterior internal bundle (AMB) and the posterior external bundle (PLB) have different stress patterns. The anterior internal bundle (AMB) mainly restricts the anterior-posterior movement of the tibia, while the posterior external bundle (PLB) mainly restricts the rotation of the tibia. The ACL has a complex functional structure and is anatomically divided into the anteromedial bundle (AM) and the posterolateral bundle (PL), which work together to maintain knee stability; the AM bundle is tense in knee flexion and relaxed in extension, while the PL bundle is tense in extension and relaxed in flexion. Conventional single-beam isometric reconstruction primarily restores AM function and does not restore rotational stability while restoring anterior knee stability. Although arthroscopic ACL single-bundle reconstruction has shown good results, it still falls short of expectations. ACL single-bundle reconstruction is not effective in restoring pre-injury motor function and has a high incidence of degenerative changes on long-term imaging follow-up, which needs to be further improved, especially in populations such as athletes. Double-bundle reconstruction, which is closer to functional anatomy, improves anterior-posterior stability and restores resistance to rotational forces better than single-bundle reconstruction, and is closer to normal ACL function. However, not all patients with ACL injuries can undergo ACL double-bundle reconstruction, for example, patients with small intercondylar fossa and difficulties in positioning the femur, which makes it difficult to establish a double attempt, usually need to adopt single-bundle reconstruction, which can also achieve considerable results.