[Objective] To investigate the clinical outcomes of Ilizarov technique combined with hamstring lengthening for severe knee flexion deformities due to spastic cerebral palsy. [Methods] A retrospective study was done on 15 children who received the Ilizarov tech- nique and hamstring lengthening for bilateral severe knee flexion deformity due to spastic cerebral palsy in our hospital from August 2017 to April 2020 and the clinical consequences were evaluated. [Results] All patients had the surgical managements conducted successfully with- out serious complications such as vascular and nerve injury. Of them, 7 patients had hip and foot deformities corrected simultaneously, in- cluding hip adductor muscle release, obturator nerve constriction, Achilles tendon lengthening and gastrocnemius aponeurotomy. The frame was adjusted only within the first 28 days after operation and was carried up continuely. The duration of wearing the Ilizarov external fixator was 36~50 days, with an average of (41.1±3.5) days. All the patients were followed up for (1.6±0.3) years. The static flexion angle of the knee at 3 months after operation and at the last follow-up was significantly less than that before operation (P＜0.05) , while the passive range of mo- tion (ROM) and active ROM were significantly increased over time (P＜0.05) . The GMFCS was improved from grade Ⅳ preoperatively to grade Ⅲ at latest follow- up. According to Herzenberg's criteria, the clinical results were marked as excellent in 9 knees and good in 21 knees, with an excellent and good rate of 100.0%. [Conclusion] The Ilizarov technique combined with hamstring lengthening is an effective treatment for severe knee flexion deformity in spastic cerebral palsy.