In order to study the influence of tooth surface micro error on gear dynamic characteristics,the rough surface was formed by using fractal theory.Associated with the factors of time-varying meshing stiffness,static transmission error and tooth friction,a nonlinear gear dynamic model considering rough surface was established.The effects of roughness,friction and working conditions on the gear dynamic characteristics were studied.The results show that when the tooth surface roughness increases,the dynamic transmission error of the gear system increases,and the dynamic performance deteriorates gradually owing to the decrease of vibration stability;the tooth friction makes the dynamic transmission error and vibration displacement of the gear pair increase,and the influence of friction on the vibration characteristics of the vertical meshing line is more obvious;the influence of tooth surface roughness on gear dynamic characteristics varies with the change of working condition,the reasonable tooth surface accuracy design combined with the working condition is beneficial to further balance the problem between processing cost and transmission quality.