( )The decomposition behaviors of methane hydrate below the ice melting point in porous media with different particle size and different pore size were studied. The silica gels with the particle size of 105-150 mu m, 150-200 mu m and 300-450 mu m, and the mean pore diameters of 12.95 nm, 17.96 nm and 3320 nm were used in the experiments. Methane recovery and temperature change curves were determined for each experiment. The hydrate decomposition process in the experiments can be divided into the depressurization period and the isobaric period. The temperature in the system decreases quickly in the depressurization process with the hydrate decomposition and reaches the lowest point in the isobaric period. The hydrate decomposition in porous media below ice-melting point is very fast and no self-perseveration effect is observed. The hydrate decomposition is influenced both by the driving force and the initial hydrate saturation. In the experiments with the high hydrate saturation, the hydrate decomposition will stop when the pressure reaches the equilibrium dissociation pressure. The stable pressure in the experiment with high hydrate saturation exceeds the equilibrium dissociation pressure of bulk hydrate and increases with the decrease of the pore size. (C) 2019 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.