To investigate the efficacy of extra-articular biceps tendon supplement (EBS) release in the treatment of valgus knee with severe flexion contracture. We retrospectively studied 27 patients who received EBS release for valgus knee combined with severe flexion contracture from 2018 to 2021. The full-length radiograph of the lower limbs in a standing position was taken before and after the operation, and the tibiofemoral angles before and after the operation were measured on the full-length radiograph of the lower limbs. Knee joint motion measurement and KSS scoring were performed before and after the operation (3 months, 6 months, and 1 year), and the obtained data were compared before and after the operation to evaluate clinical results. Compared with preoperation, postoperative HKA (p < 0.01), ROM at 3 months (p < 0.01), 6 months (p < 0.01), and 1 year (p < 0.01) were significantly improved, and KSS scores at 3 months (p < 0.01), 6 months (p < 0.01), and 1 year (p < 0.01) were significantly improved. Our EBS release has good clinical results for the treatment of valgus knee with severe flexion contracture.