<p>Sn-58Bi solder alloy, with its advantages of low cost and low melting point, has become an important subject of research in lead-free solders. However, its poor corrosion resistance remains a significant challenge in current development. Ni has been proven to enhance the corrosion resistance of tin-based lead-free solders. This study investigates the corrosion resistance of Sn-58Bi-<i>X</i>Ni (<i>X</i> = 0, 0.1, 0.2, 0.3, 0.4 wt.%) solder alloys in a 3.5 wt.% NaCl solution. The effect of Ni content on the corrosion performance of Sn-58Bi alloys was assessed using potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS), and the corrosion mechanism of Sn-58Bi-<i>X</i>Ni alloys was analyzed in conjunction with cross-sectional and surface morphology changes. The results show that when no Ni is added, the Sn-58Bi alloy exhibits the poorest corrosion resistance, with a corrosion current density of 1.414 × 10⁻⁴ A/cm² and an impedance value of 2877 Ω cm². When the Ni content is 0.1% and 0.2 wt.%, the Sn-rich phase on the alloy surface is significantly refined, and the corrosion resistance of Sn-58Bi alloy improves. This is because the addition of Ni promotes the formation of a denser and more uniform corrosion product on the solder surface. At this point, the alloy’s corrosion current densities are 5.079 × 10⁻⁵ A/cm² and 3.664 × 10⁻⁵ A/cm², with impedance values of 9904 Ω·cm² and 11,585 Ω·cm². When the Ni content increases to 0.3 and 0.4 wt.%, the improvement in corrosion resistance slightly decreases, with corrosion current densities of 8.680 × 10⁻⁵ A/cm² and 1.218 × 10⁻⁴ A/cm², and impedance values of 5918 Ω·cm² and 4764 Ω·cm². This is primarily due to electrogalvanic corrosion between the Ni₃Sn₄ intermetallic compound and the Sn-rich phase, which accelerates the dissolution of the Sn-rich phase. Therefore, Sn-58Bi-0.2Ni alloy exhibits the best corrosion resistance.</p>