To investigate the effectiveness of the reconstruction of posterior cruciate ligament (PCL) with platelet rich plasma (PRP) and 3-strand peroneal longus tendons under arthroscope. Between June 2014 and December 2017, 58 patients with PCL rupture were randomly divided into two groups: the trial group (PRP assisted reconstruction of 3-strand peroneal longus tendons) and the control group (4-strand hamstring tendon reconstruction alone), 29 cases in each group. There was no significant difference in gender, age, injury side, Kellgren-Lawrence grade, time from injury to operation, and preoperative American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score, International Knee Documentation Committee (IKDC) score, Lysholm score between the two groups ( P>0.05). Before operation, at 3 months and 12 months after operation, the IKDC score and Lysholm score of the two groups were recorded to evaluate the knee joint function, AOFAS ankle-hindfoot score was used to evaluate ankle function; KT-2000 examination (knee flexion of 90°, 30 lbs) was used to evaluate the difference of bilateral knee joint posterior relaxation at 12 months after operation, and MRI was used to evaluate ligament reconstruction; CT was used to evaluate the bone tunnel expansion of femur and tibia at 3 months and 12 months after operation. The operation was completed successfully in both groups, there was no complication in the donor tendon area. All the incisions healed by first intention. All the patients were followed up for more than 1 year. The follow-up time of the trial group was 13-17 months, with an average of 15.0 months; that of the control group was 15-20 months, with an average of 15.4 months. At 3 and 12 months after operation, there was no significant difference in AOFAS ankle-hindfoot score when compared with preoperative score and between the two groups ( P>0.05). At 3 and 12 months after operation, the IKDC score and Lysholm score of the two groups were significantly improved, and further improvement was found at 12 months when compared with at 3 months ( P<0.05); the scores in the trial group were significantly better than those of the control group ( P<0.05). At 12 months after operation, the difference of the posterior relaxation of the bilateral knees in the trial group was less than 5 mm in 27 cases, 6-10 mm in 2 cases; in the control group was less than 5 mm in 20 cases, 6-10 mm in 6 cases, and >10 mm in 3 cases; the difference between the two groups was not significant ( Z=0.606, P=0.544). At 12 months after operation, MRI of knee joint showed that all patients had good PCL graft. The MRI score of the trial group was better than that of the control group ( t=2.425, P=0.019). CT examination at 3 and 12 months after operation showed that the bone tunnel expansion of femur and tibia in the trial group were significantly better than those in the control group ( P<0.05). PRP combined with 3-stand peroneal longus tendons can significantly improve the function and stability of knee joint, effectively promote graft remodeling, and promote tendon bone healing, reduce the expansion of bone tunnel. The effectiveness is satisfactory.