Abstract: In slow-spreading ridge hydrothermal fields, multiple stage mineralization events frequently occur, resulting in complicated geochemical compositions in precipitated sulfides. At present, the mineralization mechanism of hydrothermal sulfides in the hydrothermal system remains highly debated. The Deyin hydrothermal system, located on mid-Atlantic Ridge 15°S, is a typical hydrothermal field developed on slow-spreading ridge. In this study, in-situ geochemical compositions of sulfides from the Deyin field were analyzed systematically to reveal the mineralization fluid evolution. Results show that the hydrothermal fluid temperatures increased gradually during the chimney growth, and sulfide trace element characteristics evolved from low-temperature-element enrichment to high-temperature-element enrichment, which was controlled by variable seawater mixing contents. In high-temperature mineralization stage of the chimney growth, hydrothermal fluid experienced strong phase separation, resulting in low Tl/Pb (＜0.02), Sb/Pb (＜0.5) in pyrites. This study provided new constraints on hydrothermal fluid evolution and mineralization mechanism in slow-spreading ridge hydrothermal systems.