The invention provides a photocatalysis reduction method for CO2 in flue gas in an oxygen-enriched combustion power plant, which specifically comprises the following steps of: carrying out photocatalysis reduction reaction of CO2 in flue gas between the flue gas desulfurization and the CO2 compression in the oxygen-enriched combustion power plant, and collecting liquid products obtained by reduction reaction. The invention further provides a reduction device which comprises a reaction unit, a product collecting unit and a clapboard; the reaction unit comprises a reaction chamber, wherein two ends of the reaction chamber are respectively provided with a flue gas inlet and a flue gas outlet, the reaction chamber is internally provided with a plurality of baffle plates at intervals, gas channels are formed between the baffle plates and the wall of the reaction chamber, catalyst-loaded optical fiber bundles are fixed on the baffle plates, and the top end of the reaction chamber is provided with a quartz glass plate cover plate; and the product collecting unit comprises a collecting chamber arranged under the reaction chamber, the clapboard is arranged between the reaction chamber and the collecting chamber, and holes are arranged on the positions of the clapboard, which are in one-to-one corresponding to the optical fiber bundles. According to the invention, the CO2 emission reduction and the resource utilization can be realized, and the method and the device are higher in CO2 treatment capability, low in cost, free of pollution, and low in energy consumption.