Objective To probe into the effects of the varying size of intravertebraldefect on the strength of the vertebral body under compression-flexion loading. Methods 18 vertebraes from 6 fresh cadavers were diarticulared, with their discs excised and the posterior element removed.The upper and lower adjacent vertebrae were used as controls to generate an estimate of intact middle vertebyal body strength,and the strength of the middle vertebral body with intravertebral defect were measured, which was made by a small scraper through venous aperture in the posterior edge of vertebrae. Results The result demonstrated a positive correction between vertebral body strength and the volume of the vertebral body defect. Compared with intact vertebral body,the strength of damaged vertebral body decreased 10.67%?18.00%?26.83%, with its defect rate 10%?20%?30%respectively. Conclusion The result show a positive correction between vertebral body strength and the volume of the intravertebral body defect. When the volume of cancellous interior of intravertebral body defect exceeds 30% of vertebral body volume,the patient is at risk of pathological fracture,so internal fixtion is indicated.