In this paper, the authors use the devices of frozen phase transition temperature and resistivity distribution which are self designed to elucidate the methane hydrate formation and decomposition process in the coarse sand. The results show that the processes of hydrate nucleation, formation, aggregation and decomposition can be detected accurately and efficiently by the experimental devices. The differences temperature gradients obviously influence the formation and distribution of the methane hydrate in the coarse sand. With increase of temperature gradient, the distribution of the methane hydrate becomes uneven. The methane hydrate is aggregated more easily at the apex of high-temperature while the time interval of the hydrate aggregation is shorter.