Ni–Cu–P and Cr–Cu–P steels are well known as sea water resistance steels, but the effects of alloying elements in steels on corrosion resistance are still not clear. Generally, Cr and Ni are important alloying elements for corrosion resistance but their roles in resisting pitting corrosion still need investigating. In order to understand the effects of Cr and Ni on rust layers and resistance against pitting corrosion, Ni–Cu–P and Cr–Cu–P steels were smelted in vacuum induction melting furnace and examined in the laboratory. Pitting susceptibility of two sea water resistance steels was compared by means of potentiodynamic polarization tests in 3% (mass fraction) NaCl solution. In order to evaluate the pitting propagation of steels, the simulating occluded corrosion cell tests and indoor interval hanging plate tests were performed in artificial sea water and 3% sea salt solution, respectively. The composition of inclusions, corrosive feature and characteristic of rust layer were studied by OM, electron probe micro–analyzer (EPMA), SEM and XRD. The results indicate that Ni–Cu–P steels exhibit stronger pitting susceptibility than Cr–Cu–P steels, and pitting susceptibility of two kinds of steels is not influenced by deoxidizing degrees. The results also suggest that pitting propagation rate of Cr–Cu–P steels is obviously greater than that of Ni–Cu–P steels. In acidified pits, alloying element Ni helps to enhance thermodynamic stability of matrix and improve potential of matrix. However, addition of alloying element Cr tends to lower the potential of matrix in pits. The results of rust layer analysis indicate that the compositions of inner rust layer are Fe₃O₄, α–FeOOH and a small amount of amorphous oxides. However, the rust layer of Cr–Cu–P steels is much more compact than that of Ni–Cu–P steels. It can be observed by SEM and EPMA that Cr in Cr–Cu–P steels is enriched in inner rust layer close to the matrix, while Ni is not found enrichment in inner rust layer of Ni–Cu–P steels.