Based on the beampropagation equation in free-space, the hyperbolic-fit mothed is used to calculate theM2-factor of Gaussian beams passing through a spherically aberrated lens. Meanwhile, thepower in the bucket (PIB) at the geometrical and real focal planes of Gaussian beams withspherical aberrations is also studied. Both M2-factor and PIB are chosen as the criterionfor charactering laser beam quality, detailed numeri cal calculations are performed toillustrate the effect of the spherically aberr ated lens on laser beam quality. Theresults obtained in this paper would be useful for some practical applications.