NOVELTY - Mild pre-treatment of lignocellulosic biomass raw material comprises: (a) collecting lignocellulosic biomass raw material; (b) sorting lignocellulosic biomass raw material according to raw material length; (c) cutting the sections of the lignocellulosic biomass raw material into particulates; (d) mixing the dried lignocellulosic biomass particles and water 2:1-2, preferably 1:0.5-1 and heating the mixture under atmospheric pressure; and (e) heat preserving the heated mixture, where more than 30% of the lignocellulosic biomass is decomposed into liquid solution and other 70% remains as solid.    USE - The method is useful for producing lignocellulosic ethanol or other bio-based products.    ADVANTAGE - The method is simple, economical and environment friendly, and exhibits high utilization rate.    DETAILED DESCRIPTION - Mild pre-treatment of lignocellulosic biomass raw material comprises:(a) collecting lignocellulosic biomass raw material comprising straw, garden trimmed waste, rice husk including agricultural and forestry waste, and various cellulose based energy crops; (b) sorting lignocellulosic biomass raw material according to raw material length, where the raw material length greater than 3 cm enters into step (c), and the raw material length less than 3 cm directly enters into step (d); (c) cutting the sections of the lignocellulosic biomass raw material into particulates of 2-3 cm size; (d) mixing the dried lignocellulosic biomass particles and water in a mass ratio of 2:1-2, preferably 1:0.5-1, and heating the mixture to 80-100 degrees C under atmospheric pressure; and (e) preserving the heated mixture at 80-100 degrees C for 8-10 hours, where more than 30% of the lignocellulosic biomass is decomposed into liquid solution and other 70% remains solid after preserving. The biomass mixture after processing can be directly used to produce lignocellulosic ethanol or other bio-based products by four common lignocellulosic ethanol production methods, which are stepwise hydrolysis and fermentation, simultaneous saccharification and fermentation, simultaneous saccharification and co-fermentation, and direct microbial conversion method.