Enhanced oil recovery by waterflooding is low and injected pressure is high in the ultra-low permeability reservoir, but nitrogen is easy to be injected. In this paper, core displacement experiments were conducted by the means of conventional nitrogen injection, WAG and pulse gas injection in ultra-low permeability reservoir after waterflooding. The experiment results showed that since the microanisotropy characteristic of ultra-low permeability reservoir, Nitrogen can crossflow easily in the big pore channel, therefore, injecting nitrogen normally after water flooding make an ineffective effort to enhance oil recovery. However, with using the WAG the dispersive degree of different fluid phase could be enhanced, and then, the capillary force could be formed in the advantage flow channel firstly, which make the later injected nitrogen come into partial dense area, oil recovery being enhanced effectively by 16.37%; The pulse gas injection could form pressure disturbance and interactive seepage between high-permeability zone and low-permeability zone which made the fluid redistributed in the reservoir, and finally the oil trapped in the low-permeability area was launched, thereby the oil recovery could be enhanced by 15.94%. Besides, the pulse gas injection pressure was low, and the gas injectivity was better than WAG.