  A scaling phenomenon in the cross section for fragments has been found in the
projectile fragmentation reaction, and an empirical scaling formula is proposed
by considering the dependence of cross section on the size and asymmetry of the
reaction system and the fragment itself. Furthermore, the empirical scaling
formula is used to predict the production of fragment in the
$^{68}$Ni/$^{69}$Cu/$^{72}$Zn + $^9$Be reactions around 90$A$ MeV. Compared to
the results calculated by the statistical abrasion ablation model and the {\sc
epax3} parameterizations, the empirical scaling formula can better reproduce
the measured fragments. The empirical scaling formula can be used to predict
the yield for fragment in projectile fragmentation reaction.
