In quantum information processing, an extreme high fidelity is needed. We apply a composite adiabatic passage (CAP) technique in the Landau-Zener model with harmonic interaction modulation in order to study the transition probability of the system with different model parameters. We find that this method could suppress the non-adiabatic oscillations in the transition probability and reduce the admissible error. This method could also enlarge the parameter regimes of high transition probability. Because of these good results, the Landau-Zener model with harmonic interaction modulation and CAP technique could be potentially important tools for ultrahigh-fidelity quantum information processing.