To investigate the high phenolic lignin extraction process, deep eutectic solvents based on oxalic acid and glycerol as a hydrogen bond donor were first prepared and analyzed. Two different types of deep eutectic solvent lignin and ethanol lignin were extracted using a high-pressure autoclave at different temperatures and times, and then the obtained lignin was used to prepare an ultraviolet (UV)-blocking composite film with nanofibrillated cellulose. The extract yield, phenolic hydroxyl group content, molecular weight distribution, and UV-blocking property of extracted lignin were characterized, and the UV-blocking and water-resisting properties of the lignin composite films were also analyzed. Gel permeation chromatography and phenolic hydroxyl content analysis results showed that the hydrogen bond donor type of oxalic acid cooperates with the extraction temperature of 160 degrees C as an important factor for obtaining the high phenolic hydroxyl content and uniform molecular weight lignin. UV spectrophotometer and thermogravimetry results indicated that the high phenolic hydroxyl lignin has excellent UV-blocking property, while the thermal stability of lignin may be slightly reduced. Meanwhile, in comparison to glycerol deep eutectic solvent lignin, an oxalic hydrogenbond-donor-type lignin composite film exhibited higher UV absorption and water-resisting properties with lower lignin addition.