This paper mainly numerically investigates the ultimate compression strength of un-strengthened and CFRP-strengthened steel tubes with random pitting corrosion damage. First, a developed numerical method for steel tubes with random corroded pits is introduced in detail. The accuracy of a similar numerical method is verified through the corresponding experimental measurement and numerical prediction. Then, the ultimate axial compression behavior of steel tubes with random elliptical corroded pits is numerically investigated. Several influencing factors on the ultimate strength of corroded steel tubes under axial compression load are simulated and compared, including different random distributions, region size of corroded pits, number of pits, and depth of pits. Subsequently, the method for strengthening steel tubes by using CFRPs is studied and conducted on the corroded regions of steel tubes. The reliability of steel tubes strengthened by FRP is validated through experimental and numerical results. Finally, the residual compression performance and progressive damage mechanisms of CFRP-strengthened steel tubes are researched. The different parametric influences on the strengthened performance of FRPs are simulated, including layer direction, number of composite layers, and composite materials. The results demonstrate that FRP can improve the axial compression resistance of corroded steel tubes.