The salinity of free water affects directly the formation and decomposition of methane hydrateThe phase equilibrium of methane hydrate in porous media under the condition of different compositions and concentrations of anions and cations was studied by using the orthogonal experimental designThe experimental results showed that the equilibrium temperature of methane hydrate under the same pressure conditions would decrease with the presence of ionsThe increase of ions concentration would cause the gradual decrease of equilibrium temperatureAnalysis of variance demonstrated that only Mg2+ had significant influence on the equilibrium point of methane hydrateThe influences of the concentration of three anions on the equilibrium point of methane hydrate were all significantThe induction time of methane hydrate was irregular and was rarely affected by the kind and concentration of ions