Abstract: Test steels with different cerium contents were prepared, the polarization curve and the alternating current impedance were tested, and the corrosion micro-morphology was observed. Then the immersion corrosion weightlessness experiment and the phase analysis of the corrosion products were carried out. Through such experiments, the effect of cerium on the pitting corrosion resistance of HSLA100 steel was studied. The results show that the test steel containing 0.016wt%cerium has the lowest corrosion current density, the highest pitting potential and the biggest polarization resistance;simultaneously, the observation results of the pitting morphology also show that the pitting degree of the sample is lowest, and the pitting pits are shallow and little in number. The electrochemical experiment results show that the sample containing0.016wt% cerium has the best pitting resistance. The immersion corrosion weightlessness experiment results show that the sample containing 0.016wt% cerium has the lowest corrosion rate, the inner layer of the corrosion products is composed of dense α-FeOOH and Fe₃O₄. Appropriate content of cerium benefits to form the dense Fe₃O₄ oxide film, which can restrain the exchange between ions and improve the pitting resistance.