The tribocorrosion failure mechanism of nickel-aluminium bronze (NAB) in different halide concentrations of seawater was studied using a pin-on-disc tribometer that was modified to conduct in-situ electrochemical detection during the sliding process. It has been reported that high-halide-concentration seawater provided a good lubricating effect, and thus reduced the coefficient of friction and wear rate of NAB during the tribocorrosion process. However, the existence of halide ions corroded the passive film and hindered the repassivation of the damaged areas in the wear track, resulting in an increased corrosion rate. In addition, the morphology of the wear scar revealed the occurrence of abrasive, delamination, and adhesive wear of NAB in seawater. For the whole range of halide concentration values, a positive synergy between wear and corrosion was proven, and the quantification of this synergy was discussed in detail. The results show that the corrosion- wear synergism was decreased with increasing halide concentration in seawater, and the corrosion-induced wear was dominant in the two synergistic components.