A set of bulk swirl distortion generators is designed by using a certain type of CDA profile (controllable diffusion profile) in order to investigate the effect mechanism of swirl angle generated by the stream vane swirl distortion generator and improve the design efficiency of the StreamVane swirl distortion generator. The influence of different geometric parameters and external conditions on the formation of swirl angle is studied by CFD. The results show that both the blade solidity and the installation angle have the greatest influence on the swirl angle; Relatively speaking, the outside diameter of the distortion generator and the development of the swirl flow have little influence on the generation of the swirl angle; The relationship between Mach number and swirl angle is exponential within the range of the subsonic speed studied in this paper. On the basis of the above mentioned factors, a fitting formula of swirl angle generated by the stream vane swirl distortion generator is given, and a twin swirl distortion screen is designed by using the fitting formula. The experiment result show that the fitting formula is high in reliability.