Abstract: A downward mobile gasification boiler for surface gas-phase combustion and pyrolysis of biomass briquette is provided. The boiler includes a gasification combustion chamber, a gas combustion chamber, a stranding cage slag remover, a heat exchanger, a water jacket, an air duct and an air distribution system. The air duct connected with the air distribution system is arranged in the inner cavity of the wall surface of the gasification combustion chamber. The gas combustion chamber is arranged at the upper part of the gasification combustion chamber, and an air outlet is arranged, in the middle to communicate the gas combustion chamber with the gasification combustion chamber. The lower part of a port of the gasification combustion chamber is provided with a twisting cage slag remover.