By using Zernike polynomials to describe the wavefrontdistortion of beams, the focusing performance of super Gaussian beams in far field are studied based on the generalized Huygens-Fresnel diffraction integral. The influence of astigmatism and coma on the intensity distribution at focusing position and the power in the bucket(PIB)are analyzed when the aberration of Ca system decreased to λ/13. The results show that the aberration will lead to the beam broadening at the focusing position, and the PIB in 80% decreases obviously, but the spot diameter in 95% of the energy range is still within the design value range, which meets the overall design requirement.