By using numerical solutions of the time-dependent Schrdinger equation for a one-dimensional atom in intense laser fields, We investigate the high harmonic generation and ionization of the long-range and short-range potential atoms. It is found that the intensities of high harmonic generation for both cases are similar, but the short-range potential atom does not radiate the low-order harmonic spectra, and the ionization probabilities of the long-range and short-range potential atoms as functions of the laser intensity are obviously different. Our results show that the excited states of the atom play an important role in the low-order harmonic spectra and ionization probabilities.