TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The biomass raw material is: starch raw material comprising cassava, sweet potato, corn, potatoes, wheat, rice or sorghum; or sugar raw material comprising sugar cane, molasses or beet; or cellulose raw material comprising crop straw, forest felling and wood processing residues, firewood, paper mill leftovers, paper and sugar mills containing cellulose wastes or domestic waste; or starch slag comprising starch factory residue, cheese industrial by-product and other raw materials.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The device further comprises a returning system comprising the pervaporation membrane used for treating material liquid return in a raw material jar. A pipeline is set between the pervaporation membrane system and the raw material jar. The pervaporation membrane system and the fermentation tank are used for producing and processing the raw material. The pervaporation membrane is connected to the fermentation tank by a liquid return pipeline. The pipeline is set with an upper flow meter. The device further comprises a feeding tank, a feed supplementing tank and a feeding pump. The feeding pump is connected to the fermentation tank. The pervaporation membrane system is single or multi-unit pervaporation membrane connected in series or connected in parallel, where each unit penetrates through the side of the pervaporation membrane connected in parallel to the second vacuum pump by pipeline. The porous separation membrane and pervaporation membrane is a tubular-, flat- or hollow- fiber membrane. The molecular weight cutoff of porous separation membrane is 5000-50000 Dalton or aperture is 5 mu m-1 nm. Preferred Method: The method further comprises preparing low concentration fermentation broth, and returning into the fermentation broth placed in the fermentation tank, and mixing, when the fuel alcohol fermentation concentration is reduced to a certain concentration, so as to achieve fermentation fuel alcohol concentration in the fermentation process maintaining a constant step. The low-concentration fermentation liquor is not passed as material liquid into the pervaporation membrane, but a portion of the liquid is returned to liquid material tank, and the other part of is returned to alcohol tank.