NOVELTY - Utilization of lignocellulosic biomass involves carrying out acid hydrolysis of biomass to obtain pentose solution and acid hydrolysis residue (R1); (b) treating (R1) with alkali solution to extract the alkali lignin and form alkaline hydrolysis slag (S1); (c) using cellulase to carry out enzymolysis on (S1), to obtain glucose solution and enzymolysis residue (R2); (d) returning (R2) to alkaline solution treatment or treating it with fresh acid hydrolysis residues and then carrying out the alkali solution treatment, performing step (c) and step (d) successively and repetitively.    USE - For converting lignocellulosic biomass to pentose and glucose and producing alkali lignin.    ADVANTAGE - The method is simple, and improved as compared to the existing technology, as it improves conversion rate of degradation of the lignocellulosic biomass, thus enables maximum resource utilization. The cellulase obtained from Penicillium has high activity, and improves conversion rate. The reaction avoids use of high temperature and acidic conditions without use of long reaction time thus causing less damage to lignin and cellulose. The alkali lignin is obtained in very high purity.    DETAILED DESCRIPTION - Utilization of lignocellulosic biomass involves carrying out acid hydrolysis of biomass to obtain pentose solution and acid hydrolysis residue (R1); (b) treating (R1) with alkali solution to extract the alkali lignin and form alkaline hydrolysis slag (S1); (c) using cellulase to carry out enzymolysis on (S1), to obtain glucose solution and enzymolysis residue (R2); (d) returning (R2) to alkaline solution treatment or treating it with fresh acid hydrolysis residues and then carrying out the alkali solution treatment, performing step (c) and step (d) successively and repetitively, where the cellulase is obtained by culturing Penicillium decumbens PD-G3-08, which has been preserved in Wuhan University China Centre for Type Culture Collection under the preservation number (CCTCC M2011195).