The invention relates to a biomass double-fluidized-bed catalytic gasification combined cycle power generation method taking copper slag as a circulating bed material and a system thereof, and belongsto the technical field of energy and environment. According to the method and system, biomass is heated by a high-temperature copper slag bed material in a fluidized bed gasification furnace to be pyrolyzed and gasified to generate biomass gas, biomass charcoal and tar, the tar is catalyzed by the copper slag bed material to be cracked, and the biomass gas containing a small amount of tar is purified and then utilized in a gas turbine power generation mode; the copper slag bed material and the biomass charcoal from a high-temperature cyclone separator enter a fluidized bed combustion furnace,and the high-temperature copper slag bed material heated by biomass charcoal combustion heat release returns to the fluidized bed gasification furnace; a turbine of a gas turbine is combined with high-temperature flue gas discharged by high-temperature cyclone separation, and then waste heat is recycled by adopting a waste heat boiler and an organic Rankine cycle power generation mode; in the whole process, the copper slag bed material has double functions of a heat carrier and tar catalyzing cracking, and heat energy is utilized step by step in a gas-organic working medium combined cycle power generation mode.