The conversion of lignocellulosic biomass with high content of hydroxyl groups to liquid substances with high reactivity through liquefaction was considered a promising route for realizing their high-value utilization. The competitive reaction of degradation and polycondensation in lignocellulosic biomass’s liquefaction process directly affects the liquefaction product’s characteristics. The liquefaction of Chinese Sweet Gum’s (Liquidambar formosana) fruit was carried out at various times (30, 60, 90, 120, and 150 min) using polyethylene glycol and glycerin (4∶1 V/V) as liquefaction reagents to investigate the degradation and polycondensation reaction process in liquefaction. Fourier infrared spectroscopy (FTIR) combined with principal component analysis (PCA) and X-ray diffraction (XRD) were used to characterize the liquefied residues and liquefied products. The results showed that the liquefaction efficiency gradually increased with the extension of the reaction time, and the highest liquefaction efficiency was 88.79%. The optimal liquefaction time was 120 min when the liquefaction efficiency was 87.91%, and the hydroxyl value of the liquefied product was 280 mg KOH·g-1. FTIR and XRD analysis showed that lignin and hemicellulose were priority degraded at the initial stage of the liquefaction reaction. The crystalline cellulose began degrading at a later stage, accompanied by a polycondensation reaction. Principal component analysis results suggested that the distribution of functional groups of the liquefied residues obtained at different liquefaction times was relatively independent, which could be used as the basis for judging the degradation time of each component in the liquefaction process. Moreover, the polycondensation reaction gradually became dominant after 90 min of liquefaction. In addition, to explore the feasibility of liquefaction products as biomass polyols in the polyurethane foam field, polyurethane foams were successfully prepared by adding different contents of liquefaction products (10%, 20%, and 50%). FTIR showed that liquefaction products could replace polyols in the preparation of polyurethane foam, and the addition of liquefaction products did not change the chemical structure of polyurethane foam. The study would provide a theoretical basis for further exploring the liquefaction reaction of lignocellulosic resources and the liquefaction utilization of L. formosana fruit.