Localized corrosion of steel pipe piles in the splash zone poses a critical threat to structural safety, necessitating urgent underwater reinforcement technologies. This study proposes a duplex stainless steel jacket grouting reinforcement method for locally corroded underwater steel pipe piles. Axial compression tests were conducted on nine specimens: one uncorroded specimen, three corroded specimens, and five corroded-reinforced specimens. Load-axial deformation curves, load-strain curves, and failure modes were obtained to investigate the influence of corrosion rate and stainless steel jacket thickness on bearing capacity and ductility. The experimental results indicate:1) The failure mode of unreinforced specimens was characterized by "elephant-foot-shaped" buckling failure at the bottom of the corroded region, while reinforced specimens showed inward buckling at the interface between reinforced and unreinforced zones, with no significant deformation in the grout or stainless steel jackets. 2) With an increase in the corrosion rate, the load-bearing capacity of steel pipe piles declines at an accelerating rate. 3) For specimens with corrosion rates of 10%, 20%, and 30%, the bearing capacities of reinforced piles recovered to 95%, 81.5%, and 64.8% of uncorroded levels, respectively. Notably, only the 10% corroded specimen exhibited restored ductility surpassing that of the uncorroded specimen, indicating a gradual decline in reinforcement effectiveness with higher corrosion severity. 4) Regarding jacket thickness, specimens with thicknesses of 1.8 mm, 2.4 mm, and 3.0 mm recovered to 80.7%, 81.5%, and 81.1% of the uncorroded bearing capacity, respectively, revealing minimal influence of jacket thickness on both bearing capacity and ductility under identical corrosion conditions. 5)The duplex stainless steel jacket grouting system enhances resistance to local buckling by effectively increasing the wall thickness of corroded piles, thereby mitigating strength degradation caused by corrosion-induced thinning and defects. However, the reinforcement efficacy is highly dependent on corrosion severity, emphasizing the need for tailored strategies based on specific corrosion levels in engineering practice.