[Objective] The purpose of this study was to assess the effectiveness of hamstring prolong and gradual contracture distraction with an Ilizarov external fixator in correcting and maintaining correction of knee flexion contractures of 40 degrees or greater in spastic cerebral palsy.[Methods] The medical records and radiographs of 15 consecutive pediatric patients (30 knees) with spastic cerebral palsy and knee flexion contractures of 40 degrees or greater were reviewed. The mean age of patients at surgery was 13.25 years. The knee flexion contractures were treated with hamstring prolong and an Ilizarov external fixator for gradual contracture distraction. [Results] All patients were followed-up and the mean length was 1.5(1～2.4) years.There were no serious complications .All the patients were able to walk with the aid of walking aid, and their gait improved well. The knee flexion Angle ,the degree of active and passive motion were significantly different when compared with preoperatively (P <0.05). The GMFCS grading was improved from preoperative grade Ⅳ to Ⅲ.[Conclusion] It is effective when applying ILizarov technique combined with hamstring lengthening in the treatment of severe flexion contractures in spastic cerebral palsy.