NOVELTY - Pre-treating biomass by microwave dry or semi-dry method, comprises e.g. (a) cutting and crushing to-be-processed biomass raw material, (b) scattering water to biomass according to the water content of the raw material, adjusting the water content, and uniformly mixing raw material and then stewing to make the water uniformly permeate in material, (c) weighing and putting the material into a microwave heating device, and pre-heating the material, and (d) adjusting the power of the microwave radiation between the materials when the temperature reaches 95-98 degrees C.    USE - The method is useful for pre-treating biomass, where the biomass is corn straw, rice straw, wheat straw, beanstalk, Sorghum, sweet Sorghum, crop straw, alfalfa, king grass, wood chips, small branch woody plant, silver grass or switch grass and the pre-processed biomass is useful for producing sugar, fuel, ethanol, butanol, butane diacid and liquid fuel or chemical product, solid fermentation substrate, and animal feed after pre-treating the substrate for anaerobic fermentation.    ADVANTAGE - The method is capable of pre-treating biomass with short processing time in a cost-effective manner.    DETAILED DESCRIPTION - Pre-treating biomass by microwave dry or semi-dry method, comprises (a) cutting and crushing to-be-processed biomass raw material to a grain size of 50 mm, (b) scattering water to biomass according to the water content of the raw material, adjusting the water content to 10-30 wt.%, and uniformly mixing raw material and then stewing for 1-24 hours to make the water uniformly permeate in material, (c) weighing and putting the material into a microwave heating device at a unit mass microwave radiation power of 50-1000 w/kg, and pre-heating the material for 1-10 minutes, and (d) adjusting the power of the microwave radiation to 5 kw/kg wet between the materials when the temperature reaches 95-98 degrees C, where the temperature of the material is 130-150 degrees C and the time is 10-1000 seconds to complete a process according to the different biomass raw material and pre-processing by repeating step (b) to (d) to 3 times and then increasing the processing.