Fragments produced in the reaction of 60 MeV/n 18O on Be have been measured experimentally. The isotopic distribution of fragmentation reaction is well reproduced by a modified statistical abrasion-ablation model It is predicted that the isotopic distribution shifts toward the neutron rich side for neutron rich projectile, but this isospin effect decreases with the increase of the atomic number difference Z - ZA and disappears at last, where Z and ZA are atomic numbers of the isotopic distribution and the projectile respectively.