Steel plates have been widely used in various structures, including building structures, bridges, ocean platforms, and industrial equipment. The post-buckling strength of steel plates can be substantially affected by corrosion. This study quantifies the influence of corrosion on post-buckling strength of simply supported corroded steel plates. To do so, stochastic numerical analysis is adopted, and the reliability of an established stochastic finite element model is initially verified by comparing it with the analytical results. This study also investigates the feasibility of the derived results for steel plates with different width/thickness (b/t) ratios. A variable Θ is introduced to represent the reduction factor of compression strength of corroded plates. The analytical formulas for predicting the upper and lower bounds of Θ are proposed, and the probabilistic distribution model of Θ is suggested. The method to determine the equivalent width/thickness (b/teqv) ratio of corroded steel plates is proposed. With the premise that the post-buckling strength remains unaffected, the corroded steel plates can be treated as uncorroded when the b/teqv ratio is substituted for the original b/t ratio. Conclusion of this study can establish a foundation for the buckling behavior of corroded steel plates.