Abstract: Tetrahydrothiophene in methane reference gas is the metrological foundation of natural gas odour analysis. Tetrahydrothiophene in methane reference gas is prepared by mass comparator with 0.1 mg sensitivity using gravimetric method. Because of the interaction between tetrahydrothiophene and the inner-side of the cylinder, the actual tetrahydrothiophene concentration and the result of gravimetric data exhibit some differences. Another method use manometric method to prepare reference gas and determine the concentration by total sulfur comparison. Because of the dynamic balance between tetrahydrothiophene and the cylinder, the determined concentration of tetrahydrothiophene has an uncertainty acceptable difference with the comparative result. The second method is more statistically accurate.