As far as the ultrahigh pressure expanded diameter conductor for 750 kV LGJK300/50 type is concerned, since the contact between the small strands of wire in the model are strong nonlinear point or line contact, it is difficult to find an ideal method to obtain a successful finite element model in the present literature. This paper enlarged the size of small strands of wire to 6 10 silk and tried to solve this problem. The original finite element model has been improved and the numerical simulation was carried out. The simulation results show that the present model is better than previous models, and the vibration mode of the expanded diameter conductor in engineering is mainly based on the bending and torsion deformation mode. When the model length is relatively short, the chance of breeze vibration becomes higher; when the length of model wire gets increased gradually, subspan oscillation will be highlighted, without spacing rod and the length of the wire increases gradually, and the destructive dancing follows. These are consistent with the actual operation of the project.