The invention provides high-efficiency pretreatment separation of hemicellulose from a fiber-based biomass raw material and a comprehensive utilization method. The method comprises the following steps: the forest biomass resource fiber-based biomass raw material is used as a raw material, and the fiber-based biomass raw material is firstly subjected to slurry method pretreatment: the fiber-based biomass raw material is ground by a ball mill, sieving is performed to obtain fiber-based biomass raw material powder with a certain mesh, and the powder and water are mixed according to a ratio at a room temperature to obtain a fiber-based biomass raw material powder slurry premixed liquid; through regulation and control of the reaction temperature, time and water quantity, high-efficiency hydrothermal removal of the hemicellulose in the fiber-based biomass raw material powder in the slurry fiber-based biomass raw material powder premixed liquid system is realized; after the mixed liquid is filtered, the filtrate is subjected to gradient precipitation to separate low-dispersion hemicellulose, the precipitate is dried, and the dried material is stored; after the filter residues, a polar aprotic solvent and water are mixed, the mixture is heated and stirred in a pressurized reaction kettle for a certain period of time, filtering separation is performed to obtain high-purity cellulose, the high-purity cellulose is washed by using water, drying is performed, and the dried high-purity cellulose is stored; the filtrate and water are mixed, the mixture is allowed to stand, the precipitated powder is filtered, drying is performed, and the dried material is stored; and the filtrate is subjected to reduced-pressure distillation to recover water, the solvent and a small amount of small-molecular chemicals, and recycling is performed. The method provided by the invention adopts the fast-growing forest fiber-based biomass raw material unique in China as the raw material, and has a green and environmentally-friendly process and low costs, the hemicellulose has a low dispersion degree and a high yield, the solvent used in the method can be efficiently recycled, and the method is friendly to the environment, and suitable for industrial production.