Alloying effect of Cr in the interaction with other elements in low alloy steel for corrosion resistance was designed and prepared. The corrosion behavior of the alloy immersed in mild acid–chloride solution (200 atomic ppm Cl⁻ and pH 4) at room temperature in an ambient condition has been studied by electrochemical laboratory tests (potentiodynamic polarization test, potentiostatic test, electrochemical impedance spectroscopy) and surface analyses (SEM, XPS). The results reveal that Cr addition improved the localized corrosion resistance by promoting the formation of beneficial Fe and Cu compounds on the protective films of 0.1 and 0.3 mass% Cr steels. However, the over-alloying circumstance in 0.5 mass% Cr steel caused the negative effect of Cr addition due to metal chloride-induced hydrolysis which accelerated the propagation of the localized corrosion. To summarize, 0.3 mass% Cr addition was determined to be the optimum value for alloying to blank steel.