NOVELTY - Water and ammonia based lignocellulosic biomass pretreatment method involves adding biomass and water in a high pressure reactor, hydrolyzing for 10-60 minutes at 140-220 degrees C and 0.36-6 MPa, collecting hydrolyzed liquid, then adding ammonia water in reactor, hydrolyzing for 30-120 minutes at 120-180 degrees C and 0.2-2 MPa, collecting hydrolyzed liquid, performing solid-liquid separation, cooling solid product in the reactor to room temperature, washing the reactor and solid product using water and subjecting the solid product to enzymatic hydrolysis using cellulase.    USE - The method is useful for pre-treating lignocellulosic biomass using water and ammonia (claimed). The lignocellulosic biomass is chosen from forestry waste, agricultural waste, sugar refinery waste and biomass rich in cellulose and hemicellulose.    ADVANTAGE - The method is environmentally-friendly, and utilizes lignocellulosic biomass completely, minimizes sugar loss and recycles agriculture, forestry and sugar industry wastes, and has high recovery rate.    DETAILED DESCRIPTION - Water and ammonia based lignocellulosic biomass pretreatment method involves (a) adding lignocellulosic biomass having particle size of 0.2-5 mm and water, in mass ratio of 1:5-1:20, in a high pressure reactor, hydrolyzing for 10-60 minutes at 140-220 degrees C and 0.36-6 MPa, collecting hydrolyzed liquid discharging from the reactor and performing solid-liquid separation, (b) adding 5-25 %mass ammonia water in the reactor containing biomass, where the mass ratio of biomass and ammonia water is 1:10-1:20, hydrolyzing for 30-120 minutes at 120-180 degrees C and 0.2-2 MPa, collecting hydrolyzed liquid discharging from the reactor and performing solid-liquid separation, (c) cooling solid product in the reactor to room temperature, washing the reactor and solid product using water, then discharging water from the reactor and performing solid-liquid separation, and (d) adding cellulase to the solid in the reactor and subjecting to enzymatic hydrolysis.