Abstract: The improved quantum molecular dynamics(ImQMD) model plus the GEMINI statistical decay model are used to analyze the odd-even effect of fragmentation cross sections for reactions ³⁶Ar beams on C, Al, Cu, Pb targets at 400 AMeV. The result shows that the odd–even effect is appeared in the de-excitation process of primary fragments, and the pairing energy plays an important role. The odd–even effect of fragmentation cross sections disappears when the pairing energy is removed from the de-excitation process. The odd–even effect in neutron of fragmentation cross section is significantly.