Abstract: A method and a device for making reducing sugar firstly combine a bio-substance containing lignocellulose with a solvent, thereby conducting a degradation reaction upon afore mixture through an autoclave so as to promote the bio-substance to solvent ratio during the production. Thus, a reducing sugar solution of a high concentration is produced. In the meantime, the bio-substance containing lignocellulose does not need a high-temperatured steaming after the degradation. Therefore, the water amount and the energy resources that are applied in the present invention are less than those of the conventional technique. Further, the autoclave is a common apparatus in the market, which facilitates in an easy purchase, decreases the producing cost, and benefits the product promotion.