Objective To retrospectively study the treatment methods and follow-up results of the medial collateral ligament (MCL) injury in total knee arthroplasty (TKA) surgery. Methods From January 2013 to January 2016, 612 cases (798 knees) has underwent primary TKA, 10 cases (10 knees) of which suffered from MCL injury. Among them, 7 patients were injured in the body of MCL, 2 cases in the end point of the femoral, and 1 case in the end point of the tibial. All ten patients didn't use the restrictive prosthesis and did the postoperative rehabilitation with a leg braces. We s scheduled follow-up with the patients and checked lateral stress condition after the surgery. The Knee Society Score (KSS) and range of the motion before surgery and at the last follow-up were recorded. Results The total incidence of MCL injury in this group of patients was 1.2 percent(10/798,95%CI:0.5%-2.0%). The follow-up time was 25 to 62 months (mean 46.5 months), with no case lost to follow up. There was no relaxation when extending the knee in the outpatient examination. 3 patients had mild relaxation (+) when bending the knees 30 degrees. The KSS of patients was improved from 74.5 points (52-96 points) before surgery to 149.8 points (124-172 points). The degree of activity of the knee joint was improved by an average of 78.5 °(65°-95°) to 105.5°(95°-120°), with the difference statistically significant. During the last follow-up, no patients underwent knee repair due to the medial relaxation. Conclusions We should repair the MCL positively when it was injured during the surgery. Stable internal fixation can avoid replace the restrictive prosthesis and reduce the incidence of revision due to the medial unstable.