Abstract: Based on the wave aberration theory, the relation between wave surface variance and the number of subapertures is derived when some aberration exists in single subaperture of the optical synthetic aperture imaging system. The derivation result shows that the most sensitive aberration is piston error, and then the defocusing error, tilt error, spherical aberration, coma and astigmatism. To improve the quality of the image, the defocusing error was used to balance the piston error, spherical aberration and astigmatism, and the results were significantly improved, especially the wave surface variance caused by spherical aberration was decreased by 90%. The coefficients of every aberration were decreased with the increase of the number of subapertures (N), but changed slowly when N was greater than 6. The aberration tolerance of synthetic aperture imaging system with N (N≤6) subapertures and Strehl ratio of the system with 3 subapertures were calculated according to Rayleigh criterion.