In this study, the corrosion resistance mechanism of the Te and heat treatments on martensitic stainless steel (15–5PH steel) was investigated. Heat treatment affected the dislocation density of the Te-containing 15–5PH steel and reduced its corrosion tendency. Electrochemical dissolution of the MnS-Te inclusions induced pitting corrosion. Heat treatment significantly affects the potential difference between the Te-modified inclusions and the steel matrix, consequently influencing the emergence of pitting corrosion. Heat treatment improved the anti-corrosion properties of 15–5PH steel by transforming it from an active state to a passive state. The Mott-Schottky test results show that the passive film always exhibits n-type semiconductor characteristics and that the defect density of the passive film is reduced by the heat treatment. Heat treatment facilitated the enrichment of Cr, Te, and TeO₃ in the passivation film, resulting in its improved stability and corrosion resistance. The formation of an insoluble or slowly dissolved tellurite film through Te anodic oxidation, along with the self-healing properties of TeO₃, improved the repassivation capability of the passivation film of the steel.