The invention relates to a comprehensive utilization method of a biomass raw material, and concretely relates to a method for preparing a paper pulp by utilizing the biomass raw material and recovering lignin and xylose in a black liquor. The method is characterized in that the biomass raw material is boiled through a formic acid and acetic acid mixed organic acid under the catalysis action of hydrogen peroxide, and lignin and xylose in the black liquor are recovered in the paper pulp preparation process. The whole method has a simple route by designing reasonable technological parameters, is suitable for wood raw materials, and is also suitable for grass raw materials; and a subsequent bleaching technology of the process route is simple, and the drainability of the obtained paper pulp is good.