The imaging theory and several realization ways of optical synthetic aperture telescope are presented. Based on fast Fourier transform (FFT) algorithm the point spread function and optical transfer function of a random optical synthetic aperture system are obtained, then the imaging characteristics of optical synthetic aperture telescope are analyzed from such aspects as sub-aperture configuration and arrangement, cophasing and image restoration. The influence of sparse ratio, fill factor, “practical cut-off frequency” on optical synthetic aperture telescope imaging is investigated. The analysis and simulation indicate the optical synthetic aperture technology by coherent imaging can improve the resolution dramatically compared with traditional single-aperture telescope. It is valuable for realization of lightweight and modularity of space-based optical remote sensing system.