The photocatalytic conversion of CO2 and H2O into useful chemicals or fuels over semiconductor photocatalysts is regarded as a promising technology to address the problems of global warming and energy exhaustion. However, inefficient photo-absorption and slow charge dynamics limit the CO2 photoreduction efficiency. Here, a ternary heterojunction photocatalyst, Cu2Cl(OH)3/In/In2O3 (Cu H IO), with an intimate interface is obtained via a hydrogen chemical reduction approach followed by hydrolysis reaction, where In species can be produced on the surface of In2O3 from the hydrogen chemical reaction with a calcining temperature of over 500 °C. Cu H IO exhibits enhanced photocatalytic activity for CO2 conversion compared to pristine In2O3, In2O3 with In species (H IO), and Cu2Cl(OH)3/In2O3 (Cu IO). In the absence of sacrificial agent or cocatalyst, the yield rates of CO and CH4 over Cu H IO are 4.36 and 1.09 μmol g-1 h-1, which are 8.38-fold and 18-fold that of pristine In2O3 (0.52 and 0.06 μmol g-1 h-1), respectively. The photocatalytic performance enhancement of Cu H IO results from the construction of the ternary heterojunction, with synchronous improvement in the photoresponse and charge separation of In2O3. Moreover, the possible CO2 reduction pathway over Cu H IO has also been investigated and proposed. This work provides an important strategy for developing a high-efficiency heterojunction photocatalyst system for solar fuel generation.