Abstract“Nanhai I” shipwreck of China Southern Song Dynasty is the oldest and the most integrally preserved shipwreck in the world. The related conservation and archeological research have caught great attention of different experts all over the world. In this study, different types of concretion covered on the surface of the ceramics in “Nanhai I” shipwreck were analyzed by X‐ray diffractometer, micro‐Raman spectrometer, and scanning electron microscope equipped with energy dispersive spectroscopy. Based on the analyses, we found that the grey concretion was mainly composed of quartz, aragonite, and calcite while the reddish concretion was mainly composed of pyrite and quartz. Our study indicated that the formation process of the grey concretion probably included the crystallization and transformation of aragonite, while the corrosion of iron implements and crystallization of pyrite were highly involved in the formation of reddish concretion.