This paper presents a new approach to modify the surface of the Ti-6Al-4V alloy fabricated by additive manufacturing. This method is particularly suitable for titanium or titanium alloy components with complex shapes (such as pipes, holes and internal flow paths) which are difficult to be polished by conventional methods. The corresponding electrochemical tests were carried out in Hanks' balanced salt solution. The results demonstrated that the chemical polishing of additively manufactured Ti-6Al-4V obtained a high-quality surface through the combination of oxidation corrosive action and polishing liquid flow by reducing the peak-to-valley spacing and smoothing the alloy surface. After chemical polishing, a passivation film consisted of rutile and anatase formed on the alloy surface, which showed n-type semiconductor characteristics and had a lower donor density, leading to the increase in the corrosion resistance.