Abstract: Greenhouse gases (GHGs), such as CO2, released from the combustion of fossil fuels have led to a continuous rise in the global average temperature, which has led to the focus of research on CO2 abatement and resource utilisation technologies. Photocatalytic CO2 reduction technology is considered to be a promising technology for solving environmental and energy problems at the same time, as the energy required for the reaction is taken from renewable solar energy, and CO2 can be converted into hydrocarbon fuels or high-value chemicals, realising an ‘artificial carbon cycle’. In terms of product modulation, the selective synthesis of multicarbon (C2+) compounds has become a frontier in the field of photocatalytic CO2 reduction due to their higher energy density, better storage and transport properties, and significant economic added value. The generally low C2+ selectivity of existing systems is mainly limited by the difficulty of stabilising key intermediates. Bimetallic active site construction provides a new idea to solve this problem by synergistically reinforcing the intermediate adsorption capacity, which can both optimize the adsorption activation of *CO and provide hydrogenation sites to promote the conversion of CO2 to hydrocarbons. Among many photocatalytic materials, tin dioxide (SnO2) stands out with the advantages of broad spectral absorption, low cost and chemical stability, but its practical application is still limited by two technical bottlenecks, namely, narrow UV response range and high photogenerated carrier complex rate. The intermetallic synergistic effect formed by palladium-gallium (GaPd) bimetallic doping modification promotes the charge separation and carrier transport, which effectively improves the photocatalytic CO2 reduction performance of SnO2. The introduction of Ga sites forms more CO adsorption species on the surface. These adsorbed CO molecules were able to migrate to the neighbouring Ga-Pd bimetallic active sites under photoexcitation conditions, and *CO provided sufficient intermediate concentration for C-C coupling and subsequent hydrogenation reaction on the bimetallic sites, which in turn improved the selectivity of C2 products. The co-doped modified photocatalysts reduced CO2 products with CH4, CO, C2H4 and C2H6, and the optimal catalyst Ga0.4Pd0.6/SnO2 had the largest total carbon yield of 5.81 μmol/g and the selectivity of the C2 product of 25.4%. The key intermediates (*CO, *COCO, *CH3, and *CH3CH2O) for the generation of C2 were observed by in situ diffuse reflectance Fourier transform infrared spectroscopy, and it was revealed that the generation of C2 products in bimetallic doping was closely related to the formation of intermediates.