The invention discloses a method and a device for purifying VOCs (Volatile Organic Compounds) through gas-phase photolysis and liquid-phase photocatalytic oxidation. The method comprises the following steps: S1, gas-phase photolysis: irradiating the VOCs under an UV (Ultraviolet)-light condition, enabling the photolysis time to be less than 1s, generating ozone by reaction, and forming a mixed gas by the ozone and a residual gas after photolysis; S2, liquid-phase photocatalysis: carrying out reverse gas-liquid contact on the mixed gas obtained in S1 and catalyst slurry, enabling the mixed gas to fully react with the catalyst slurry, and enabling the mixed gas to be converted into CO2 and H2O. According to the method for purifying the VOCs through the gas-phase photolysis and the liquid-phase photocatalytic oxidation, disclosed by the invention, the gas-phase photolysis and the liquid-phase photocatalytic oxidation are effectively combined, and the two steps influence each other, work together and cannot be divided; the problems of catalyst deactivation and low liquid-phase absorption efficiency of the VOCs due to deposition of an intermediate product on a gas-solid catalytic surface are fundamentally solved; through a synergistic effect of multiple processes of high-energy ultraviolet photolysis, the liquid-phase photocatalysis, ozone catalytic oxidation and the like, the generation and the deposition of the intermediate product are reduced, and efficient and stable degradation of organic waste gas is realized.