To better understand the response of authigenic minerals in sediments in a gas hydrate system, a total of 652 sediment samples recovered from IODP Expedition 311 were washed and all authigenic pyrites were picked. SEM photographs show that pyrites occurred in the form of both micro-spheroids and cubic crystal aggregations, caused by microbial fossilization and inorganic processes, respectively. The stable sulfur isotopic compositions seem to have a wide range of delta (super 34) S CDT values from -35.4 ppm to +53.6 ppm for the processes of anaerobic oxidation of methane (AOM). Sea salt sulfate in the upper part of the sediment column was predominantly reduced by AOM, and the remaining sulfate involved in reduction would probably have caused the positive sulfur isotopic excursion of pyrites. In the cold vent, delta (super 34) S CDT values increase gradually with depth from -35.83 ppm near the top to 32.49 ppm at depth, indicating that more remaining sulfates were involved in reduction under higher methane flux and more intensive AOM. This study will have an important impact on exploration for potential marine gas hydrates in China and on deciphering the ancient methane-derived sedimentary record.