By using potent iodynamic polarization method, the current study reveals the corrosion inhibition ability of polyaspartic acid(PASP) on carbon steel in 20% phosphoric acid solution. The results show that the inhibition efficiency of PASP increase sig nificantly at 20 e with the increasing of PASP concentration. The inhibitor efficiency Greaches as high as 76.65% with the PASP concentration of 1.0 g/ L. In PASP-SDS system, the maximum inhibition efficiency is found to be 78.66% when combining PASP and SDS at the same concent ration of 0.25 g / L; which indicates a positive synerg istic effect. This work also proves that the anode inhibit ion reaction contributes most to the inhibitive effect of PASP.