Extensive calculations on isoscaling behavior with the sequential-decay model GEMINI are performed for the mediate-heavy nuclei in the mass range A = 110 and at excitation energies of up to 3 MeV per nucleon.Isoscaling can still be observed after entire-step decays are considered for the light products as in the only first-step decay process case.Comparison between the products after the first-step decay and the ones after entire-step decay demonstrates that multi-step secondary sequential decay strongly influences the isoscaling parameters α,β as well as the fragment isospin distribution.After entire-step decays, the isoscaling parameters α and β are decreased and the fragment isospin distribution can better reproduce the isospin distribution shape as the experimental data.