The invention discloses a new method for comprehensive utilization of straws, and in particular relates to a new method for separation of sugar acid solution in straw hydrolysis liquid and comprehensive utilization of a straw resource. When the problem of the separation of sugar acid is solved, a series of high value-added products such as biomass-based colloidal carbon spheres, nano carbon black, high specific area nano porous carbon spheres and high-energy organic carbon are prepared. The method comprises the following steps: hydrolyzing the straws by using organic acid at certain concentration, and filtering the mixture to obtain the sugar acid solution and filter residue; adjusting the concentration of the sugar acid solution, and performing polycondensation and carbonization reaction to prepare the colloidal carbon spheres; and thermally treating the prepared colloidal carbon spheres to form the nano carbon black; or activating the colloidal carbon spheres under certain conditions to form nano porous carbon with high specific area and strong adsorption capability. Compared with the colloidal carbon prepared from high molecular materials and cyclic polysaccharide, the biomass-based colloidal carbon spheres and other products prepared by the method have the characteristics of large raw material amount, reproduction, energy conservation, recycle of sulfuric acid and phosphoric acid, environmental protection of the whole process and the like.