The electrochemical conversion of CO(2) into liquid fuels is a promising strategy for achieving carbon neutrality. Tin dioxide (SnO(2)) shows a notable ability to electrocatalytically convert CO(2) into formate, though its efficiency is significantly limited by its low catalytic activity. Herein, we construct facet-oriented SnO(2) nanoflowers all standing on a three-dimensional nickel hollow fiber that exhibits superior CO(2)-to-formate electrocatalytic performance. A formate selectivity of 94% and stability of 300 h with a current density of 1.3 A cm(-2) at -1.1 V (vs. reversible hydrogen electrode [RHE]) are attained under ambient conditions. Notably, an extremely high CO(2) single-pass conversion rate of 85% is achieved, outperforming prominent catalysts reported in electrocatalysis. The synergetic combination of the unique nanostructures and their advanced spatial configuration is proposed to be responsible for the facet-oriented SnO(2) with a hierarchical structure, providing fully exposed active sites and facilitating mass and charge transfers. Enhanced mass transfer in the hollow fiber electrode verified by electrochemical measurements and well-retained Sn(4+) species confirmed by in situ spectroscopy synergistically boost the high CO(2) conversion activity. In situ spectroscopy and theoretical calculation results demonstrate that the SnO(2)(101) facet favors ∗OCHO intermediate formation and ∗HCOOH desorption, leading to high formate selectivity. This study provides a straightforward approach to the precise fabrication of composite hollow fiber electrodes, enabling highly efficient electrocatalytic reactions with gas molecules.