Objective To explore the effectiveness of one-stage posterior medial corner (PMC) repair or reconstruction combined with anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) reconstruction in the treatment of knee dislocation (KD)-ⅢM dislocation. Methods The clinical data of 15 patients with knee KD-ⅢM dislocation who met the selection criteria between January 2016 and July 2019 were retrospectively analyzed. There were 9 males and 6 females, aged 22-61 years (mean, 40.3 years). Injuries were caused by violence of flexion, valgus, and external rotation, including 10 cases of traffic accident injuries, 3 cases of crush injuries, 1 case of winch injury, and 1 case of explosion injury. The time from injury to operation was 3 days to 6 months, with an average of 18.5 days. Acute PMC repair combined with PCL+ACL reconstruction was performed in 10 cases in acute stage, including 3 cases of irreducible dislocation. PMC+PCL+ACL reconstruction was performed in 5 cases with chronic dislocation (dislocation time more than 3 weeks). Before operation and at last follow-up, the knee joint function was evaluated by Lysholm score and International Knee Documentation Committee (IKDC) score. KT-3000 was used to evaluate the forward stability of the knee (calculated the difference of tibial anterior displacement of both knees), the X-ray film of the stress position of the knee joint was used to evaluate the valgus of the knee (calculated the difference of medial joint space width of both knees) and the backward stability (calculated the difference of tibial posterior displacement of both knees), and the internal and external rotation stability was evaluated by 30° tibial external rotation and 90° knee flexion internal tibial tests (calculated the difference of tibial internal rotation and the difference of tibial external rotation of both knees). Results The operation time was 120-240 minutes, with an average of 186.5 minutes. Patients were followed up 24-48 months, with an average of 27.4 months. There was no complication such as infection, deep vein thrombosis, vascular injury, and heterotopic ossification occurred. At last follow-up, the Lysholm score, IKDC score, the difference of tibial anterior displacement of both knees, the difference of medial joint space width of both knees, the difference of tibial posterior displacement of both knees, the difference of tibial internal rotation and the difference of tibial external rotation of both knees were significantly improved when compared with preoperative ones (P<0.05). According to the IKDC valgus stability grading standard, there were 3 cases of grade C and 12 cases of grade D before operation, and 10 cases of grade A and 5 cases of grade B at last follow-up, which was significantly improved when compared with that before operation (Z=−4.930, P=0.000). At last follow-up, the pivot shift test of 15 patients was negative. The anterior and posterior drawer tests of 10 patients were negative, 5 patients had mild instability, both the anterior and posterior drawer tests were (+). Conclusion KD-ⅢM dislocation of the knee joint can lead to instability of the posterior medial and anterior knee joints. Acute dislocation combined with dimple sign requires surgical reduction as soon as possible to repair PMC and reconstruct PCL+ACL. In chronic patients, PMC is difficult to repair, it is recommended to reconstruct PMC+PCL+ACL at one stage to improve knee joint stability. The early and middle effectiveness are satisfactory.