Abstract: In order to study effect of wavefront aberration on focusing characteristics of ultrashort femtosecond laser pulses, based on Rayleigh-Sommerfeld scalar diffraction theory, focusing characteristics of ultrashort femtosecond laser pulses with uniform intensity distribution and Gaussian intensity distribution were compared and studied under different wavefront aberration, such as defocusing, astigmatism, coma aberration, trilobe aberration and spherical aberration. The results show that, wavefront aberration has an obvious adverse effect on intensity distribution of femtosecond pulses with uniform intensity distribution at the focal plane. The peak power of focusing femtosecond pulses is reduced. However, the influence of femtosecond pulses with Gaussian intensity distribution is relatively small. Under Gaussian intensity distribution, it is still possible to obtain better focusing spot near diffraction limit at focal plane. At the non-focal plane, even if the initial pulse has Gaussian intensity distribution, intensity distribution at the non-focal plane is also affected by various wavefront aberration. For 30fs (1/e² half width) ultrashort pulse in this paper, the effect of wavefront aberration on pulse duration is almost negligible. The results are of practical significance for the evaluation of beam quality and the analysis of focusing characteristics of ultrashort femtosecond laser beams.