Positions and diameters of sub-aperture in optical synthetic aperture array are two important factor for imaging. The characteristics of point spread function, optical transfer function and diffraction image of several different optimized linear array configuration of optical aperture synthesis with aberration-free are discussed by using an approach based on ratio of diameter of sub-aperture to length of arrays. The results of simulated computation show that cover of spatial frequencies for optical transfer function are very different for different position of sub-aperture. The bigger the diameter of sub-aperture is, the more complete the spatial frequency covers. But when the ratio exceeds some extent, the spatial frequencies will be redundant and cost of system construction will increase. Besides, increase of sub-aperture can decrease the intensity of the ghost images and intensified the quality of imaging. The results show that the factors of diameter of sub-aperture and total length of arrays must be taken into account in the optimizations.