By solving the 1 dimensional time dependent Schrodinger equation, the above threshold ionization (ATI) and high order harmonic generation (HOHG) of atom under different laser intensity are obtained, and the relation between the ATI and HOHG is discussed. The results show that under higher laser intensity, both the ATI and HOHG have plateau and cutoff, but under lower laser intensity, the HOHG has plateau and the ATI decreases monotonically.