The invention discloses a method for alkali metal peroxide to carry out gaseous phase carbon dioxide photoreduction. The alkali metal peroxide X2O2 (X=Li, Na, K, Rb and Cs) with strong oxidizing property carries out the reductive transformation of gaseous phase carbon dioxide under ultraviolet irradiation and a water participation condition so as to reduce CO2 into CO; a water consumption amount in reduction reaction is regulated to control the time of duration of reaction that carbon dioxide is reduced to carbonic oxide, so that reduced product-carbonic oxide is subjected to long-time linear growth, and optimal activity can be obtained when the mole ratio of water and peroxide is 1:1; in addition, under the condition, the reduction reaction can be kept to be continuously and stably carried out for a long time. The method has the advantages that photo-reduction materials are simple and easily obtained and a reaction system is simple. The reduction reaction can be continuously carried out only through the control of a reaction condition. The method has the potential which can be applied to industrial production and has a wide prospect.