This paper focuses on Q355B steel under the condition of local anti-corrosion coating failure to explore the rusting behavior of the steel and its impact on mechanical properties. Standard specimens in three typical local anti-corrosion coating failure modes, namely pitting corrosion, banded corrosion, and surface corrosion, were designed. Based on electrochemical tests, the rusting rate of the steel under the local anti-corrosion coating failure modes was measured, and the rusting morphology and distribution characteristics of the steel were analyzed. The starting points, propagation paths, and morphological changes of local rusting were analyzed based on the test results, and the corrosion paths and mechanisms under the local anti-corrosion coating failure modes were revealed through the corrosion surface morphology. The elastic modulus, yield point, yield strength, tensile strength, ultimate strain, and elongation after fracture of the steel under the local anti-corrosion coating failure modes were analyzed through the steel tensile tests. The results indicate that, the reduction coefficients of the elastic modulus, yield strength, and tensile strength of the steel under the local anti-corrosion coating failure modes have a linear negative correlation with the average corrosion rate; the reduction coefficients of the ultimate strain and elongation after fracture have a nonlinear correlation with the average corrosion rate. This study reveals the influence of local anti-corrosion coating failure modes on the mechanical properties of the steel, and the research results can provide references for the anti-corrosion protection of steel and the structural safety assessment.