<p>Photocatalytic CO₂ reduction is considered an attractive route to simultaneously address the sustainable energy crises and environmental issues. However, obtaining excellent CO₂ photoreduction property is restricted by the great challenges of low separation efficiency of photo-excited carrier, narrow light absorption range, sluggish charge transfer kinetics, and low CO₂ adsorption/activation ability. Herein, a series of Co_SA-TT-COF/CdS (the synthesized covalent organic framework (COF) material is denoted as TT-COF) organic/inorganic S-scheme heterojunction photocatalysts are successfully synthesized for CO₂-to-CO photoconversion by integrating Co single atoms (Co_SA) decorated COFs with cadmium sulfide (CdS) nanotubes via an <i>in situ</i> condensation combined with a post-modification strategy. Specifically, the regulation of the thickness of the TT-COF layer on the surface of CdS optimizes the active site density and accessibility, thereby boosting the CO₂ photoreduction efficiency. The Co_SA-TT-COF/15 wt%CdS heterojunction photocatalyst (50.5 nm in TT-COF thickness) dramatically achieves the excellent CO production rate as high as 14157 µmol g⁻¹ h⁻¹ and selectivity of 90.9%, which is one of the best COFs-based photocatalysts reported thus far. Theoretical calculation, experimental results, and femtosecond transient absorption spectroscopy reveal that the construction of S-scheme heterojunction between Co_SA-TT-COF and CdS leads to an enhanced built-in electric field, suitable hybrid energy levels, small energy bandgaps, extended light-harvesting range, enhanced visible-light absorption, preeminent photo-excited carrier separation ability, accelerated charge transfer kinetics, and decreased energy barriers for CO₂ adsorption/activation, directly contributing to the superior CO₂ photoreduction performance.</p>