It will be important to predict as accurately as possible the remaining strength reduction in future for drawing reasonable maintenance scenario in aging steel structures. Since local corrosion damage often appears depending on structural details in members, it will be thought that corrosion progress according to corrosion environment and periodic inspection results must be considered to remaining strength estimation. In this study, the bending strength analyses of corroded H-shape weathering steel which had been used for 20 years, were conducted for future prediction of remaining strength reduction by using local corrosion surface data generated numerically. A simple corrosion progress model was applied for generating surface irregularities. In this model, it assumes that corrosion surface is formed by falling down a number of attack factors to discretized objective area on steel surface. Also, attack factors will be able to decide from some control parameters by referring actual corrosion state. Moreover, this model can consider locational concentration of attack factors by adopting appropriate probability distribution referred the contour maps of remaining thickness for actual local corrosion surfaces. From the analytical results, both remaining strength and torsional buckling behavior of upper flange with artificial corroded surface were almost the same to experimental results. Also, it will be predicted that remaining strength after 30 years from now was decreased as about 38% than initial state.