In order to research the influence of the excitation of variable speed and damping on subway gear transmission system,the subway helical gears model of the bend- torsion- axes is built,and the model considered the time- varying meshing stiffness,gear meshing error,backlash nonlinearity and torque of outside parameters during the subway working. After the dimensionless processing and normalized equation of six degree of freedom dynamics model,used the numerical analysis of the gear dynamics model is carried out by using the variable step forth order Runge- Kutta numerical integration method,the gear system dynamic response state diagram is obtained. With the help of time history diagrams,phase plots,Poincare maps and the bifurcation diagram,the system evolutionary process of periodic motions,quasi- periodic motions,bifurcation and chaotic motions with the change of the system excitation frequency and mashing damping ratio are qualitatively analyzed. The results show that subway helical gear system is more stable under the high speed and meshing damping ratio. Finally,its correctness is verified by experiments.