To assess the deterioration of various performances of railway steel bridges in service caused by environmental corrosion, the numerical simulation approach is adopted to restore the corrosion morphology and analyze the degradation of mechanical properties of steel bridge components after corrosion. Based on the background of Lanyu Yellow River Iron Bridge in Central China, through the investigation of domestic and foreign scholars’ research on corrosion morphology, and according to the existing statistical data of pitting depth, the random distribution model of pitting depth, pitting size and pitting location of different pits was established by using Python scripting language. Combined with ABAQUS secondary development, the random pitting solid model of fine mesh division was established. By analyzing the influence trend of different shape pits on stress concentration effect, it is found that semi-ellipsoidal pits have the most obvious influence on stress concentration. Therefore, semi-ellipsoidal pits are selected to establish a random distribution entity model of pitting corrosion, and the deterioration trend of uniaxial tensile mechanical properties of specimens under different corrosion degrees is studied. The results show that the stress-strain curve of the specimen decreases with the increase of the surface corrosion rate and gradually becomes obvious with the increase of the corrosion time. In the initial stage of corrosion, the tensile properties of the specimen are less affected by the surface corrosion rate, and after the corrosion time becomes longer, the corrosion degree of the specimen becomes more serious, and the deterioration trend of the tensile properties becomes more obvious. The ultimate strength of components decreases with the increase of surface corrosion rate and average corrosion depth. The effects of both should be considered comprehensively when considering the ultimate strength reduction after corrosion.