Down-looking synthetic aperture imaging ladar (SAIL), with a transmitter of direct wave-front transformation in inner optical fields by parallel scanning, makes use of self-heterodyne detection to improve the resolution of images. Wave-front aberration in inner optical fields has effects on the imaging quality of the down-looking SAIL because the optical fields on the target plane depend on the inner optical fields at the focal plane of main lens. Zernike polynomials are proposed to represent wave-front aberrations. The influence of primary aberrations on down-looking SAIL imaging is investigated. The results show that focus, astigmatism, coma and spherical aberrations have significant influence on imaging, and the deeper the aberrations are, the more significant the influence on the resolution of images is. When the root mean square (RMS) value of primary aberrations is less than 0.05λ, the influence on resolution of images is very small. When the RMS value is up to 0.25λ, the resolution of images is up to 3 times in the condition of astigmatism and coma aberrations. Meanwhile, the target pointing at different positions has different resolutions with coma and spherical aberrations. The further the imaging targets from the center position are, the more significant the influence on the resolution of images is.