This paper presents a numerical study on the compressive behavior of steel pipe piles repaired with patch plates welded underwater. In this study, a uniform thickness reduction is assumed for a portion of a pipe pile to simulate corrosion damage, and a special attention is paid to modeling the mechanical behavior of fillet welds in finite element analysis based on available experimental data. Effectiveness of different welding patterns on pipe piles with various size parameters is examined in terms of stiffness, load-carrying capacity, and load share ratio of patch plates of repaired piles. Effectiveness of transverse welds in the repair is also examined, and equations to calculate a load share ratio of patch plates, the minimum thickness of patch plates, and the maximum number of slits are proposed for the repair design.