Abstract: Using the second-order-moment and entropy-based definitions of the beam width, changes of the beam parameters including beam width, far-field divergence angle and beam quality factor of flat-topped beams passing through a spherically aberrated lens are studied. It is shown that the spherical aberration affects the beam parameters in the image space. The relative errors of the beam width and far-field divergence angle introduced by the spherical aberration increase with increasing spherical aberration coefficient and decreasing beam order. The spherical aberration results in an increase of the beam quality factor of flat-topped beams. The relative errors of the waist width at the real focal plane depend on the sign of the spherical aberration coefficient, whereas the relative errors of the