Efficient fractionation of woody biomass provides an opportunity to separate and then upgrade each of the cellulose, hemicellulose and lignin fractions. The current processes for the fractionation of biomass target high-quality cellulose or lignin solely. Here, we developed a simple and efficient strategy for achieving high-quality cellulose and lignin simultaneously from woody biomass. Solvent thermal treatment was used to release the lignin and hemicellulose fragments from beech sawdust. 92.8% cellulose was retained in cellulose pulp with the purity of cellulose as high as 93.5% and a highly crystalline structure, using tetrahydrofurfuryl alcohol (THFA) and water as the solvent. In addition, 77.4% pure lignin powder was recovered. A linear correlation between the lignin monomer yield and the percentage of total β-O-4 or condensed linkages was observed during the lignin depolymerization process. Our strategy offers a possibility for the high-value utilization of whole biomass.