Accurate modeling of the dynamic stall phenomena is very important for transient aerodynamic load prediction of wind turbines. The Beddoes-Leishman dynamic stall model was presented through modeling the effects of attached flow and separated flow in the paper. Based on the Beddoes-Leishman model, a program for dynamic stall analysis was developed and integrated into the existing wind turbine aerodynamic load prediction software. Applying the developed program, the dynamic stall characteristics of NACA 63-418 airfoil were calculated. And the effects of changing mean angle, reduced frequency, and Mach number were studied. The power generation load case of a 1.5 MW variable speed pitch-regulated wind turbine was simulated. The result indicates that dynamic stall possesses significant influence on the transient aerodynamic load.