DFT+U calculations have been utilized to explore theoretically three potential pathways of HCHO oxidation on Co-doped CeO2(111) with O-vacancy herein. To begin with possible adsorption configurations and resultant adsorption strengths of HCHO on Co-doped CeO2(111) are presented, we conclude that HCHO adsorbed Co-doped CeO2(111) has the kinetic stability order of Eads(Co-O-bridge) > Eads(O-top) > Eads(Ce-top-II) > Eads(Ce-O-bridge) > Eads(Ce-top-I) > Eads(Co-top) with different adsorption locations. O-vacancy has further constructed artificially at the surface rather than subsurface to stimulate the catalytic activity of Co-doped CeO2(111) because of surficial lower O-vacancy formation energy compared to the subsurface. Based on Langmuir-Hinshelwood mechanism in which O2 and HCHO are both co-adsorbed on the reduced ceria surface, three resultant individual reaction products, resulting from different pathways of HCHO oxidation on Co-doped CeO2(111) with O-vacancy, are identified in detail within the frame of transition state theory. It shows that, at Co-O bridge site, HCHO is oxidized to carbonate species with reactive energy barriers of TS1 of 0.71 and TS2 of 0.36 eV; at O top site, HCHO oxidized to CO need to overcome barriers of TS1 of 0.55 and TS2 of 0.06 eV; while at Ce-O bridge site, HCHO to CO2 is the most difficult to proceed because of its highest energy barriers of TS1 of 0.96 and TS2 of 2.14 eV. We thus predict that the reaction pathway of HCHO to CO proceeds with the lowest overall barrier on defective Co-doped CeO2(111). These findings provide clear insight into further exploration in formaldehyde activation processes.