The development of high-value utilization paths for agricultural and forestry waste was highly consistent with the major strategic demand to “further promote green and low-carbon energy transformation”. In this paper, the objective was to investigate the pathway of propanediol (PG) and diethylene glycol (DEG) liquefaction catalyzed by phosphoric acid of cellulose from corn stalk at atmosphere pressure, aiming at understanding the mechanism of lignocellulosic biomass liquefaction reaction under the action of acid-catalyzed polyhydroxy alcohols. The chemical groups, molecular weight and distribution, molecular structure, and pyrolyzation of cellulosebiofuels were analyzed by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectra (NMR), gelpermeation chromatography (GPC), and thermo gravimetric analysis (TGA). FTIR showed that the biofuels had similar FTIR characteristics. At the early liquefaction stage, cellulose degradation produced more hydrocarbons, ethers, and carbonyl compounds. At the later stage of liquefaction, the carbohydrate degradation products, hydroxyl or olefin in cellulose, reacted with PG/DEG to generate organic matter insoluble in 1, 4-dioxane. GPC explained that with the progress of the reaction, the breakage degree of the cellulose molecular chain would be aggravated, and more and more low molecular weight (LMW) substances were generated by degradation. However, when the reaction time reached a certain value, the degradation products reacted with PG/DEG to produce larger molecular weight substances, resulting in the molecular weight of biofuel no longer being reduced. Results from 1H- and 13C-NMR presented that cellulose was degraded under liquefaction, and the molecular chain was broken, but part of the glucose structure was still preserved. With the reaction, these structural units were transformed again to produce LMW compounds. When the reaction continues, polymerization reactions could occur between these products or with PG/DEG, forming new substances with consistent structures and gradually stable properties. The results of TGA showed that the biofuel contained 70%~85% compounds with carbon number less than 25 and 5%~10% compounds with carbon number more than 25. In conclusion, this paper revealed the liquefaction reaction process of cellulose by studying the structural changes in the liquefaction process of polyhydric alcohols, which laid a theoretical foundation for exploring the liquefaction mechanism of corn stalk whole components.