Since there is no testing standard for mercury content determination in wellhead natural gas or raw natural gas with liquid hydrocarbon or water in the world, to eliminate the interference of aromatic hydrocarbons, the author proposes a direct determination method according to the characteristics that mercury in natural gas is almost all elemental mercury. This method firsts get the value with mercury and interference, and then the value only with interference with a filter which only adsorbing mercury. By subtraction of two values, the real mercury content will be got. Research shows that this method is not only stable and comparable, but also is easy to master, and is not only suitable for product gas, but also for raw natural gas.