NOVELTY - A biomass gasification ash and burning ash quenching liquid is soaked, and then dried. The low-temperature catalytic pyrolysis is provided in the pyrolysis device using indirect heat supply flue gas, to obtain pyrolysis coke and pyrolysis gas. The ash outlet is provided in the gasification dust hopper bottom, and solid particles are separated, to obtain crude synthesis gas. The obtained crude synthetic gas is entered into gas separation device and separated, to obtain high methane gas. The gasifier ash is quenched with water in combustion, to obtain methane-rich gas.    USE - Preparation of methane-rich gas by catalytic gasification of biomass.    ADVANTAGE - The methane-rich gas is efficiently prepared with high gasification efficiency, and reduced water consumption, by simple method.    DETAILED DESCRIPTION - A biomass gasification ash and burning ash quenching liquid primary shower is soaked, and then dried. The low-temperature catalytic pyrolysis is provided in the pyrolysis device using indirect heat supply flue gas, to obtain pyrolysis coke and pyrolysis gas. The outlet flue gas is emptied through flue gas purifying system, and pressurized catalytic gasification of biomass generated in the pyrolysis reactor, and pyrolysis coke are provided into the gasification reactor in a steam/oxygen atmosphere. The ash outlet is provided in the gasification dust hopper bottom, and solid particles are separated, to obtain crude synthesis gas. The solid particles are provided into the combustion reactor, obtained crude synthetic gas is entered into the gas separation device and separated, to obtain high methane gas. The portion of hydrogen-rich gas is separated in the gasification reactor, biomass pyrolysis gases generated in the pyrolysis reactor is provided into the combustion reactor, solid particles are separated, to obtain cofiring combustion ash. The gasifier ash is quenched with water in the combustion discharged by water quenching and solid-liquid separation, to obtain methane-rich gas.