Objective To compare the biomechanical performance of pedicle screws with different forms in lower thoracic and lumbar vertebra. Methods 54 vertebral specimens were obtained from 6 fresh normal frozen cadavers (T9-L5). The experimental 5.5 mm conical pedicle screw was implanted at one side at random and tested with an MTS machine (858 Bionix Ⅱ). To measure the maximal insertion torque firstand then the maximal pull-out strength. The same experiment was done with the cylindrical screw of 5.5 mm on the other side. Then the revision test with 6.25 mm and 7.0mm pedicle screws was done in the lumbar region. Strength dada were recorded. Results At lower thoracic region the torque of conical screw(1.445±0.66) N.m was distinctly higher than that of the cylindrical screw(1.073±0.42) N.m(P<0.05),but in the lumbar region such difference was not found. Conical and cylindrical screws have similar pull?-out strength. Correlation between insertion torque and pull -out strength was statistically significant with the cylindrical screw(r=0.629), but not with the conical screw (r=0.179). The displacement when reach the maximal pull-out strength was similar for the screws with the different forms. Conclusion The conical screw has the similar pull-out strength with that of the same diameter cylindrical screw. And if the diameter of conical screw is similar with the inner-diameter of pedicle, it has the higher insertion torque. The relationship between the insertion torque and pull-out strength is based on the different screw form.