Vortex generators can restrain wind turbine flow separation and effectively delay stall,transition has an important impact on its performance. An unsteady numerical simulation using Gamma-Theta transition model has been made to investigate the influence of transition on wind turbine DU91-W2-250 and the transition rule with vortex generators. It is shown an inclusion that Full turbulence model undervalue the lift coefficient and overvalue the drag coefficient of wind turbine with vortex generators,the maximum relative error of lift coefficient is 23.1% and the maximum relative error of lift-drag ratio is 51.8%,the Gamma-Theta transition model can accurately simulate the performance of the wind turbine with vortex generator,the maximum relative error of lift coefficient is only 7.9%. Vortex generators make an obvious three-dimensional transition phenomenon on the surface of blade,the effect of the internal transition is more obvious and the effect of inhibiting flow separation is more effective. The area of separation with transition model is smaller in the same condition. Delay of the blade stall is also more obvious,the separation has been effectively controlled to have a great effect on the performance.