To verify the biomechanic performance of auto-compress locking nail(ALN) in femoral shaft fracture therapy, to provide reliable basis for clinical use. Methods' 9 fresh cadaveric femurs were used,the biomechanic properties of compression,bending and torsion were analysed using electric measuring apparatus after fixation of fracture. Resultst @ALN was similar to GK nail in strength, stiffness and stability(p>0.05); @The stress shielding rate of ALN was significantly smaller than that of GK nail; @ALN had reasonable mechanic distribution, low stress shielding rate and fixation stability, also was easy to operate with rapid rehabilitation. Conclusion: ALN not only have the same properties of anti-bending, anti-shearing,anti-torsion and anti-rotation as GK nails but also have auto-compress elastic fixation. In clinic, rigid fixation(interlocking intramedullary nail) has no enough stress conduction in fracture region, elastic fixation(cloverleaf type intramedullary nail)can not effective ly control bending, shearing, torsion and rotation stress in fracture region, ALN have successfully resolved the contradiction. It is one kind of new interfixation instrument with good performance.