On the basis of the theory of interferometric imaging, this paper introduces the theory of optical synthetic aperture imaging technique. Then, two types of synthetic aperture imaging systems, Michelson interferometry and Fizeau interferometry, are compared in imaging processes, imaging characteristics, sizes of visual field and the scopes of application, and the present situation and developing trends of both Michelson and Fizeau synthetic aperture telescopic systems for ground based and spacebased are described. It points out that the development of the former will focus on the long and complex base line structures and the latter will emphasize the complex apeature arragement to form a equivalent aperture that is several times or tens times that of original one. Compared to traditional optical systems, the optical synthetic aperture system is characterized by its high resolving powers， small mass and costs and easy to be folded, so it is a useful approach to higher resolving powers. Finally, it is proposed that several kinds of new techniques such as lucky imaging, launching by module and assembly in an orbit, unsupported membranes can be also introduced into the synthetic aperture imaging technique.