To provide theoretical basis for clinic bone lengthening. Methods: 20 immature New Zealand white rabbits were used in this part of the study. A configuration type distractor and force transducers was assembled on each side of distal epiphyseal cartilage of femur for application of mechanical tensinn force. Half animals made circumferential periosteal division in the proximal epiphysis. The measurement of the bone,X-ray film and KS-400 Image Analysis System were used to study the morphology and cellular proliferation of the epiphysial cartilage after 4 weeks of distraction. Result: The low tensile stress increase in length of the distracted femur and increase in thickness of the epiphyseal carting. Cell proliferation in the physis occurs in the proliferative and hypertrophic zones. No statistical difference were found in both groups which had had circumferential periosteal division and had not. Conclusion: The low tensil stress had stimulating effects on the proliferative activity of the epiphyseal cartilage. Tension force combined with ciroumferential periosteal division did not approach significant enhanced growth effects.