In view of their particular damage to the marine archaeological wood, the iron sulfides in the shipwrecks Huaguang Reef I of the Southern Song Dynasty were analyzed by X-ray diffraction (XRD), Inductively coupled plasma-Atomic emission spectrometry (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The results showed that the samples contained a lot of Fe and S, which distributed throughout all the wood and even in the 4cm depth. And the two elements exist as oxidized iron, iron sulfides, sulfates, or other reduced sulfur. It was also showed that the main forms of iron sulfides were FeS and FeS2, and part of iron sulfides had been oxidized to sulfates. Thus, much more attention should been paid on the control of iron sulfides in the subsequent conservation process to prolong the time of heritage preservation.