The phase transmission process of received radiation signals is analyzed. And the passive synthetic aperture imaging is compared with traditional optical synthetic aperture imaging,and the spatial resolution factor is defined based on array scaling factor. By the study of spatial resolutions of the antenna array and the fiber array,the influence of spatial resolution factor and array scaling factor on the spatial resolution in whole imaging system are discussed,and the spatial resolution equation is deduced for passive synthetic aperture imaging systems. Then the influences of array scaling factor and received radiation direction on the system′ spatial resolution are investigated respectively by simulations and calculations. In the end,the significances of the research results about the spatial resolution are emphasized in designing passive synthetic aperture photonic imaging systems.