A metering device and metering method for metering carbon dioxide flow belong to the technical field of preparation of polyurethane foam materials. The metering device of the present invention has a simple structure and a small size, can accurately control the amount of the delivered liquefied carbon dioxide; meanwhile, one end of the metering pump is connected with the sliding block, and the sliding block can move on the transverse plate, thus changing the vertical movement stroke of the piston rod and changing the flow volume of the carbon dioxide. The cylinder of the metering pump of the present invention is internally provided with the water passages, and a coolant can be filled into the water passages to keep the temperature of the carbon dioxide constant.