A system and method deliver fluidized powder based on flue gas carrying waste slag and instant cooling steel slag. A first flue gas pipeline receives pressurized CO2-rich flue gas and in fluid communication with a fluidization air pipeline, a pressurization air pipeline and a supplementary air pipeline respectively and through them enters an upper discharge bin; a second flue gas pipeline receives the pressurized CO2-rich flue gas and in fluid communication with a gas-gas mixer, a dense phase discharge guide pipe first end extends into the upper discharge bin and receives high-pressure dense phase gas-powder flow of CO2-rich flue gas, and a dense phase discharge guide pipe second end is connected to the gas-gas mixer; a variable-pitch twin screw sealed conveyor discharge end extends into an upper discharge bin internal space, and is provided with an upwardly inclined gas-blocking segment.