OBJECTIVE To investigate the bending mechanical properties and provide reference for orthodontists to select the proper wires during alignment stage. METHODS In order to analyze the load deflection rate of NiTi round wire quantitatively, some NiTi round wires of different cross-sectional dimension (0.36, 0.41, 0.46 mm) were selected. Then loading-unloading experiments were carried out with the micro-orthodontic archwire testing apparatus and double end bending test could be accomplished with the wire in a 0.56 mm x 0.71 mm standard incisor edgewise bracket slot. RESULTS Under the load of 0.03 N.m, 0.36 and 0.41 mm NiTi round wire showed excellent super-elasticity, while 0.46 mm NiTi round wire didn't. When the optimal moment produced by the archwire was between 0.01 N.m and 0.02 N.m, the bending range of 0.36, 0.41 and 0.46 mm NiTi round wires was from 21.0 degrees to 49.5 degrees , 7.2 degrees to 23.7 degrees , and 6.5 degrees to 9.5 degrees , respectively after deducting the contact angle. CONCLUSIONS On the premises of yielding effective orthodontic force, the preferable NiTi round wire for alignment was the one which could produce continuous and slowly declining force.