The fragmentation cross sections of reactions 12C+2H,12C,14N,16O at beam energies from 50 to 100 MeV/nucleon are investigated using the isospin-dependent Boltzmann-Langevin equation model.It is found that fragment species increase approximately with the increasing target mass.The fragment species and some fragments production cross sections in reactions of 12C+12C,14N,16O show an obvious variation at the beam energies from 50 to 80 MeV/nucleon.However the calculated fragment production cross sections do not change much when the incident energy increases from 80 to 100 MeV/nucleon.