Although dielectric barrier discharge (DBD) plasma is a promising technique for CO2 conversion, realizing CO2-to-alcohol is still challenging via the use of H2O. Herein, for the first time, efficient CO2 conversion was achieved via the synergism between the Cs2SnCl6 photocatalyst and DBD plasma assisted by H2O. The CO2 conversion ratio of plasma photocatalysis was 6.5% higher than that of only the plasma and photocatalysis, implying that the synergism of plasma catalysis and photocatalysis was achieved. Furthermore, the DBD plasma assisted by the Cs2SnCl6 photocatalyst could convert CO2 and H2O to CO and a small amount of methanol and ethanol. The CO2 conversion ratio was enhanced by 50.6% in the presence of H2O, which was attributed to the improvement of charge transfer due to the increased electrical conductivity of the photocatalyst surface during plasma discharge. This work provides a new idea for developing an efficient system for CO2 utilization.