Electrochemcial reduction of CO₂ (CO₂RR) into the industrial feedstocks and low carbon fuels could be a promising strategy to alleviate the excessive emission of CO₂. In CO₂RR, C1 products are more feasible due to their low electron transfer and relative fast kinetics. A flexible SnO₂@CC catalyst electrode was synthesized by one-step hydrothermal method in alkaline condition and annealing in air at high temperature using CC as supporting material, SnCl₂ 2H₂O as SnO_x precursor and sodium citrate as stabilizer. The electrocatalytic performance of catalytic electrode compared with that of traditional gas diffusion electrodes (GDE). Pure SnO₂/GDE and commercial SnO₂/GDE were prepared by traditional spraying technology. Among different GDEs, the 3D layered SnO₂@CC catalyst electrode had more catalytic active sites and faster charge transfer rate, which resulted in higher electrocatalytic activity and formic acid selectivity. The maximum current density at -1.45 V vs. SHE is -46.4 mA cm^-2, and the Faraday efficiency for HCOO^- is 73.4% at -1.3 V vs. SHE.