By means of ABAQUS software, the finite element model of a section of a real transmission line was set up, and the stresses and the deformations of the line under typical cases were numerically analyzed. According to collapsing details of the tower, a three dimensional solid finite element model of the local structure, in which the details of the structural link, bolt pre-tightening force and the clearance between bolts and screw holes were considered, was established, and the model was connected with the other portion of the tower discretized by beam and truss elements to obtain the integrity of tower. Moreover, the effects of the bolt pre-tightening force on the slipping of the bolt and structural stress were numerically investigated. It is concluded that insufficient bolt pre-tightening force gives rise to obvious slipping and large structural stress. Therefore, insufficient bolt pre-tightening force is probably one of the main reasons leading to tower collapse.