Abstract: Wind turbine normally occurs dynamic stall due to wind shear,yaw,pitch and other factors. In the six-dimensional motions,surge motion has a significant impact on the aerodynamic characteristics of floating wind turbine,and the influence law of its dynamic stall characteristics are worth discussing. The SST k-ω turbulence model with the γ-Reθtransition model and dynamic grid technique are used to study dynamic stall characteristics of S809 airfoil under the influence of compound motion（surge+pitch）. The results show that,surge motion enlarges the hysteresis loop of the lift and drag coefficient. The lift coefficient increases and drag coefficient decreases in the pitching up stage,and the fluctuating amplitude is proportional to the amplitude of surge. The lift coefficients decrease in the pitching down stage. By changing energy of the airfoil boundary layer,surge effectively reduces the topology of the trailing edge vortex,enhances the induction effect of the leading-edge vortex,and weakens the dynamic stall degree of the airfoil in the pitching up stage.This study reveals the dynamic stall characteristics of airfoil under surge motion,which is important to accurately understand and evaluate the aerodynamic performance of floating wind turbine.