Objective To construct a 3D nonlinear finite element model and analyze the biomechanics of the space closure by using preajusted直丝弓?? appliance with sliding mechanics. Method With the whole digital model including denture, periodontal tissue, wire and appliance直丝弓? set up by using laser scanning, 3D reconstruction and computer aid design technology, a finite element model was constructed. To make the nonlinear calculation by setting up the contacts between teeth and contacts between wire and brackets as contact relationship.R esults The distribution of stress in periodontal is lower and well-distributed. There existed only 1 contact point and 1.4N contact normal force at the first molar. The initial displacement of anterior teeth is more than that of posterior teeth. All this has made the wire more easier to sliding. Conclusions The results from the model are basically corresponded to the results from the clinic study, which proved the validity of the model and could be the groundwork for the further sudy on some more biomechanical problems about continuous wire.