To study on the significance and basis of acidolysis index to China marine gas hydrate exploring, since 2006, 111 samples derived from Leg 164 and 204 of the Ocean Drilling Program (ODP) were analyzed in the experiment center of China Petroleum Exploration Research Institute to obtain data on acidolysis hydrocarbon index and methane carbon isotopes by the gas chromatography (GC) of PE AutoSystem XL and isotope mass spectrometer (IRMS) of Finnigan MAT251. Through these, we study the reliability of the acidolysis method and characterize the gas hydrate potential. The results show that the acidolysis hydrocarbon index has a stable correspondence with the Gas Hydrate Stability Zone (GHSZ) in the ODP, and that there are clear abnormal signs in shallow samples that might reliably reflect the existence of authigenic carbonate caused by hydrocarbon migration from bottom hydrate. We therefore propose that the ability to characterize the acidolysis hydrocarbon is crucial to submarine gas hydrate exploration in China.