Abstract: A simple model for DNA molecules is proposed.The dynamical mechanism of the nonlinear localized excitation is studied by Runge-Kutta method.The large amplitude motion is simulated for N coupling base pairs of DNA molecules.The physical picture of the nonlinear localized excitation and its stable propagation can be emerged by means of adopting suitable parameters of Hamiltonian and time stpe.The nonlinear interaction on the beather effect is also discussed.