Abstract: The number of design variables and their design room are focused on in airfoil parameterization. Fewer variables helps improve the speed of convergence and adequate design room can help to find the best result. However, they contradict with each other. A research was carried on the performances of basic Bezier-Spline curves and a comparison was presented between different orders of Bezier-Spline curves in order to explain their ability of describing a supercritical airfoil and aerodynamic errors as a result of geometric errors. An adding-order airfoil parameterization method was put forward based on the characteristics of Bezier-Spline curves. An optimization design system of expanding design room was established combined with improved particle swarm optimization algorithm which guarantees design room and efficiency. The method balances the inconsistency of design quality and efficiency. By comparing the results of a typical airfoil optimization using the proposed method and the traditional Hicks-Henne model function method, feasibility and high efficiency of this method is verified.