Abstract: Distortion caused by gripping and cutting usually exists in weak rigidity part machining. Clamping force is difficult to control with traditional clamping method, which will cause distortion uncontrollable. A new method based on lateral clamping device is raised to ensure machining accuracy. By calculating pressing force and machining force, appropriate clamping force could be applied, therefore distortion will be in acceptable range and machining will keep steady simultaneously. The machining result shows that flatness and dimensional accuracy has achieved design requirement.