The asteroids are the most important small bodies in the solar system, while the movement of the near-earth-asteroids (NEAs) is specially concerned by the world. The focus on these asteroids is that they encounter the earth. The orbital evolution of this kind of asteroid is studied by analyzing and comparing them; reasonable dynamical models and corresponding algorithm are given, and the formal numbered NEAs are calculated. The results of the minimal distance and the very close-approach time with the earth agree well with those announced by the Minor Planet Center (MPC).