Considering the complex and changing load environment works characteristic of planetary gear transmission system of 2. 5 MW wind turbine caused by random wind speed,by using the two parameters Weibull distribution,the time- varying wind load caused by random wind speed is obtained. A Dynamics model of 2. 5 MW wind turbine planetary gear transmission system is built by using lumped- parameter method.Considering the internal excitation such as the time- varying meshing stiffness and bearing stiffness,the numerical method is used to simulate the dynamics performance of planetary gear transmission system for 2. 5 MW wind turbine. The vibration displacement and vibration velocity of components in system which are influenced by time- varying input torque are got. The research results can lay a good theoretical foundation for fault diagnosis and optimization design for wind turbine gearbox.