This paper aimed to develop a new strengthening method using carbon fiber reinforced polymer (CFRP) strand sheet for port steel structures of which structural performance had been degraded by corrosion. Because CFRP strand sheet is bonded to steel members with specially-purposed epoxy lining material, the proposed method can be applied to the steel members submerged in sea water. From the result of the axial tension test, the bond capacity between steel plate and CFRP strand sheet showed enough performance to resist the axial tension stress when the corrosion products are perfectly removed from the plate surface before bonding. The strengthened plate was possible to consider as a steel-CFRP composite member if the cross-sectional loss of steel plate was less than 50%. In addition, the sectional stress generated by the bending test of corroded steel pipe was decreased by applying the proposed method. However, the effect of strengthening by proposed method was greatly affected by the condition of stress transmission between steel pipe – epoxy lining material – CFRP strand sheet.