Based on the quasi-static aerodynamic theory, the oscillator model of two-degree-of-freedom motion on the subspan oscillation for bundle conductor was built and the vibration equations were derived. The numerical analysis wad carried out on the basic of stability theory and the mechanism research on subspan oscillation for bundle conductor was made. Firstly, the nonlinear vibration equations were linearized. Then, the stability of the system was determined according to eigenvalue analysis. The MATLAB program of the subspan oscillation for bundle conductor was compiled. The critical wind speed has been studied under the Hopf dynamic bifurcation theory and Hopf static bifurcation theory and different damping ratio. The relationship between critical wind speed and frequency ratio was given. Finally, the advices were given on the control of the subspan oscillation for bundle conductor.