Abstract: In order to improve the enzymatic saccharification ratio of straw when producing biomass ethanol, rice straw was pretreated with ethanol-phosphoric acid solution at the normal temperature and pressure. The effects of temperature, ethanol volume fraction, time and the recycled ethanol-phosphoric acid solution on enzymatic saccharification ratio of rice straw were investigated. The results showed that the enzymatic saccharification ratio of rice straw increased from 10.03% to 57.75% when the volume fraction of ethanol was 50% (v/v), the pretreated temperature was50℃ and the pretreated time was 60 min. The enzymatic saccharification ratio of straw pretreated with the recycled ethanol-phosphoric acid solution was reached 56.89%, and close to saccharification ratio of straw pretreated with ethanol-phosphoric acid. The pretreatment with the recycled ethanol-phosphoric acid solution was able to reduce energy consumption and save operating cost with reducing the number of recycling ethanol by distillation. The physical structure and chemical properties of rice straw were changed after pretreated. The crystalline structure of rice straw was destroyed during the process of pretreatment, and its specific surface area and porosity increased. The pretreated straw was easily hydrolyzed by hydrolytic enzymes or microbe. Ethanol, lignin, phosphoric acid and other useful materials in filtrate solution were easily separated by distillation and centrifugation. The research could provide a circulatory pretreatment way of straw under mildness conditions was obtained.