Abstract: A description of the synthetic experiment of methane hydrate is given in this paper, along with a preliminary study of ion concentration changes during the process, whilst providing important technical support for the gas hydrate geochemical exploration. In this article, the development of a set of experimental devices, which simulate the formation process of methane hydrate, is also discussed in this paper. The position and shape of hydrate, the reaction time, the temperature and pressure of the experiments were observed during methane hydrate formation. The concentrations of major ions including K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^-, SO₄^2- were continuously detected during the process to investigate the relationship among the major ion concentrations, temperature and pressure. The results show that methane hydrate forms randomly in seawater. It may have a different nucleation and agglomeration process of hydrate under the same initial conditions. There was a good positive linear relationship between the ions variation and methane gas consumption in the system with the correlation coefficients between 0.9848 to 0.9950, which was not affected by the formation position and morphology of the hydrate. The ion content had small differences under the same gas consumption in the microenvironment of the methane hydrate formation process. These important features provide the basis to make a preliminary estimate of gas consumption by using the major ion content in pore water around the methane hydrate.