The performances of three kinds of spatial arrangement for the optical synthetic aperture imaging system with four sub-apertures are analyzed. Based on the criterion of avoiding the loss of the effective spatial-frequency information, the restrictive conditions of the spatial arrangement are calculated, and then the effective frequency coverage range and the equivalent aperture are obtained. The results shows that three-arm arrangement is adopted as long as the requirement of frequency coverage range is relatively high; when the frequency coverage range of the three-arm arrangement and the annular-uniform arrangement is equal, the former is better than the latter based on the criterion of the secondary peak depression. When the frequency coverage range of the three-arm arrangement and the annular-optimization arrangement is equal, the point spread function of the annular-optimization arrangement is larger than that of the three-arm arrangement, and the optical transfer function of the annular-optimization arrangement is lack of symmetry of three-arrangement.