The invention relates to a biomass biological syrup preparing method. The biomass biological syrup preparing method comprises taking biomass materials as the raw material to preprocess and screen thebiomass material to obtain certain-mesh biomass materials; drying the certain-mesh biomass materials, weighing out a certain quantity of the certain-mesh biomass materials to prepare a suspension of acertain concentration, regulating the pH of the suspension, keeping the temperature, adding in a certain amount of composite enzymes of pectinase and feruloyl esterase, stirring the mixture as a certain rotating speed for enzymolysis for a while, regulating the pH and keeping a certain temperature, and adding in a certain quantity of composite enzymes of cellulase, lytic polysaccharide monooxygenases (LPMO) and catalase and a quantity of L-ascorbic acid for enzymolysis for a while. The biomass biological syrup preparing method shortens the enzymolysis time, reduces the adding amount of enzymes, prolongs enzyme activity maintenance, achieves reutilization of the enzymes, reduces the cost and the like to prepare high-concentration enzymolyzed syrup.