The analysis samples of natural methane gas were collected from three gas field areas of marine sedimentary environments， i. e. from the northeast and west parts of Sichuan Province and the west part of Hubei Province. Ratios of hydrogen isotope composition of Individual hydrocarbon are determined and compared with each other under the control of the error less than 5‰ with the standard gas by a gas-water equilibrium method. An analysis result is worthy to pay attention that the hydrogen isotope in methane from Puguang Gas Field in the northeast part of Sichuan has an average δD value of -126‰(SWOM), which is about 40‰ heavier than that of -164‰（SWOM）of the hydrogen isotope in methane available from Tahe Oil Field in Tarim Basin. This phenomenon is deemed to be closely relative with the δD value of coexisting formation water and also directly associated with the maturity of natural methane gas.