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Wheat straw(WS)was pretreated by four organosolv pretreatment methods-Formiline process pretreatment(Formiline),Acetoline process pretreatment(Acetoline),Sulfuric acid-catalyzed ethanol organosolv pretreatment(SACE)and Auto-catalyzed ethanol organosolv pretreatment(ACE).Optimal operation conditions of Formiline and Acetoline were obtained.Then the main chemical compositions,physical structure changes and cellulose digestibility of the wheat straw pretreated under respectively optimized conditions were compared and mass balance was conducted.Results indicated: Formiline,SACE,ACE recovered more than 90%of cellulose as solid phase; Formiline and Acetoline removed a part of lignin while SACE and ACE changed lignin structure; the structure of pretreated WS became loose and disordered,which is beneficial to enzymatic hydrolysis; ACE pretreated WS had the lowest crystallinity index may due to ethanol can destroy or alter crystallinity of cellulose; SACE pretreated WS reached the highest glucan conversion rate(GCR)(60.80%)in a short hydrolysis time(12h)while Formiline pretreated WS reached the highest GCR after a relatively long time(more than 48h); adding low concentration tween 20(0.5g/L)had a certain role in promoting enzymatic hydrolysis for organosolv pretreated wheat straw,but high concentration tween 20(5g/L)had less promoting effect or even inhibition effect except for Acetoline pretreated wheat straw; 100g raw material pretreated could be converted to most glucose and cellulose(26.55g)during a relatively short hydrolysis time(24h)by SACE while least by Acetoline.Further investigations are required to determine which method is more economic.