Anterior cruciate ligament injury is a common clinical injury, and most of them are combined with lateral collateral ligament and meniscus injury, which seriously affects the knee function, work, life and sports of patients. Arthroscopic ACL reconstruction is an effective treatment method with fast recovery and good clinical results, and whether correct and careful rehabilitation training can be implemented after surgery is closely related to the restoration of joint function and prevention of postoperative complications. The specific rehabilitation training steps are as follows: a. On the day of surgery, after the anesthesia subsides, active flexion and extension exercises of the toe and ankle joints should be started, with forceful, slow, maximum plantar flexion and dorsiflexion of the ankle joint. The quadriceps contraction and straight leg raising exercises were performed 1-2 days after surgery. Contraction of quadriceps muscle is the driving part of knee extension activity, which can prevent muscle wasting atrophy and deep vein thrombosis. The functional exercise of CPM machine was performed 3 days after surgery, generally starting from 30° and increasing by 5° every other day, twice a day, 30-60 min each time, until the amplitude reached about 100°, based on the principle of gradual progress. 4. 4 weeks after surgery, active knee extension and flexion training was started, 30-60 min each time, 2-3 times a day, until the knee was flexed to 110°. V. After the swelling subsides, weight-bearing training can be started gradually. Generally, partial weight-bearing with the crutches is started from 3~4 weeks according to the tolerance condition, gradually to full weight-bearing, and after 3~8 weeks, the crutches are abandoned for weight-bearing walking. Then, squat training was performed to strengthen the quadriceps muscles. The patient was asked to place the toe of the affected limb against the foot of the bed to control the foot from moving forward and maintain stability, and then spread both feet shoulder-width apart, straighten the upper body, grasp the bed rail with both hands and squat, 5-6 times a day for 5-10 min each time. It should be noted that the knee joint should be protected with a joint brace for 3 months at discharge, and the brace should be removed 3 months after surgery to strengthen muscle strength and endurance. After 6 months, the patient can resume all daily activities, such as bicycling, swimming, jumping rope, jogging, etc. He can also perform impact sports, such as playing ball and bouncing sports, and return to the preoperative level of sports after 1 year.