Abstract: The vibration caused by broken wire can be calculated with pseudo-static method, but dynamic longitudinal tension responses can not be calculated by this means. To avoid this disadvantage, explicit dynamic finite element method was presented. Results indicate that the displacement as well as non-balanced load responses from broken lines are larger at bottom of insulator string which approaches broken-line span, and responses weaken rapidly with the distance increasing from broken-point. The peak of dynamic tension response is 1.5―2.5 times of the initial tension and the amplified factor is growing with the distance increasing. The static tension response is 0.26―0.95 times of initial tension. The unloading function is dropping with the distance increasing from broken-point. In addition, the influence of some parameters on transmission line system responses, such as initial tension of wire, span between two neighbor towers, length of insulator string have also been investigated.