The invention discloses a double-layer mechanical grate type garbage gasification incinerator and its boiler power generation system, including a double-layer garbage gasification incinerator, a boiler system, a circulating air supply system, a power generation system, and a double-layer garbage gasification incinerator The ember furnace is located directly below the gasification furnace, and the gasification furnace and the upper end of the ember furnace are provided with flue gas outlets. The boiler system includes a boiler body, and the boiler body has a cyclone combustion chamber, furnace chamber a, furnace chamber b, and cyclone A water-cooled wall is set in the combustion chamber, a superheater is set in the furnace room a, an evaporator is set in the furnace room b, a steam drum is set on the top of the boiler body, and the superheater outputs superheated steam; the power generation system includes a steam turbine, a generator, a steam input pipe, and a steam turbine The output end is sequentially connected to the condenser, water pump, low-pressure steam-water heater, deaerator, booster water pump, and high-pressure steam-water heater. The first and second-stage water-steam separators and the first and second-stage high-pressure Steam heater.