The high order harmonic generation (HHG) of nitrogen molecule irradiated by ultra-intense femto-second pulsed laser is simulated by the time dependent density functional theory (TDDFT) method with the general gradient approximation of the exchange-correlation energy. The effect of different laser polarization direction on HHG is discussed. The results indicate that the HHG spectrum of N2 has similar characteristics as the typical atom HHG spectrum. With the increase of the angle θ　between laser polarization direction and molecular axis, the spectral intensity of HHG decreases, which is in agreement with the experimental result by J.Itatanl published in Nature.