In order to study the dynamic characteristics of gear transmission system of wind turbine with random wind and the effect of random backlash on system stability, a stochastic volatility model is established to obtain the external excitation of gear transmission system of wind turbine. A dynamic model of system is set up with the consideration of gear time-varying mesh stiffness, transmission error and backlash. The dynamic behavior of system with random wind and the effect of random backlash on system stability are obtained using numerical method. The results show that: (1) The vibration displacement of system components has the similar trends with external excitation, and the higher the speed, the greater the vibration displacement. (2) Random backlash has a significantly influence on system stability. The instability of system decreases at first and then increases with the increase of mean backlash, and the stability of system decrease with the increase of standard deviation of backlash. The operation stability of a wind turbine will improve if select an appropriate gear backlash.