Group velocity mismatching and group velocity dispersion of fs laser pulse in CsLiB6O10 crystal are analyzed. The coupled equations of ultra-short pulse SHG are deduced by Fourier transform. The second harmonic pumped by 532 nm, 50 fs fundamental wave through CLBO is simulated numerically. The results show that the group velocity delay of second harmonic is about 100 fs at 266 nm through 0.5 mm lengths CsLiB6O10 and the second harmonic shape is widened linearly with the increase of crystal length. The group velocity mismatching Δβ(2)1=226.243 fs/mm, and lowness and second order group velocity dispersion β(2)2=210.120 fs2/mm, β(3)2=65.587 fs3/mm are reported for second harmonic on CsLiB6O10 crystal. The results indicate that group velocity mismatching and group velocity dispersion lead to the widening and defomation of the harmonic.