Aiming at the current serial design where the variable pitch control and airfoil of vertical axis wind turbines (VAWTs) are independent of each other, which fails to maximize the aerodynamic performance of wind turbines, a modified actuator cylinder model (ACM) based on the Beddoes-Leishman (B-L) model and the zero wind speed drag coefficient was presented. The accuracy of this modified model was verified by experimental data. Secondly, an airfoil optimization design method for VAWTs based on the modified ACM model and the novel dual-sinusoidal variable pitch regulation law was proposed. The particle swarm optimization (PSO) algorithm was used for the optimization design, and the class-shape transformation (CST) method was adopted to realize the parametric characterization of the airfoil. Taking the CST coefficients and variable pitch trigonometric function coefficients as design variables, and maximizing the power coefficient as the objective function, the optimization was carried out. The optimization results show that the new airfoil obtained by optimization has a maximum lift coefficient increases by 9.60% compared with the original airfoil, and an average lift-drag ratio increased by 20.82% compared with the original airfoil. Compared with the VAWT with zero pitch angle and original airfoil, the VAWT with synchronously optimized airfoil and variable pitch angle has a power coefficient of 0.352 2, which is increased by 20.66%. The synchronous optimization of variable pitch law and airfoil has a significant effect on performance improvement, verifying the feasibility of this method and providing a new idea for the design of variable pitch law and airfoil for VAWTs.