Recently, formate of possible abiogenic origin has been reported from uncatalyzed transfer hydrogenation of CO₂ with glycerine under alkaline hydrothermal conditions. However, little is known about the mechanism for production of abiogenic formate from CO₂ and lactate from glycerine during such processes. Herein, we investigated the formation of abiogenic formate from CO₂, D₂O solvent effect, reactor materials effect and H₂O molecule catalysis for uncatalyzed transfer hydrogenation of CO₂ with glycerine under alkaline hydrothermal conditions, and then have proposed and proved the potential reaction mechanism. The present work should help facilitate studies on industrial applications of CO₂ reduction using abundant alcohol compounds as reducing materials rather than hydrogen, and the development of renewable high-valued chemicals from alternative biomass derivatives and the primary greenhouse gas to fossil fuel.