The fast steering mirror is an important optical component of adaptive optics, the structure properties of shafting fast steering mirror and no-shafting fast steering mirror are compared, the difference working and application characteristics are analyzed, a new structure of fast steering mirror is designed on this basis. The flexible bearing has the characteristics of no friction and big angle, the shafting uses these characteristics. The applicable parameters are proposed and the relative flexible bearing is selected by analyzing and calculating. The design combines the advantages of shafting fast steering mirror and no-shafting fast steering mirror, a structure of the fast steering mirror which has a development prospect is proposed.