tSteam explosion is one of the leading and most promising biorefinery technologies for lignocellulosicbiomass. Water as the only transfer medium participated in steam explosion process is closely correlatedwith refining efficacy and energy consumption, while researches on steam explosion are neglected fromtransfer mechanism. In this work, from water transfer perspective, steam explosion process was inno-vatively divided into four specific stages and the multi-stage mass transfer model of steam explosionprocess was firstly established. From this model, quantitative relation of water composition in each stageand final water content formula were evaluated, which is efficient to guide the process energy efficiencywith several proposed regulation strategies. By combining transfer process simulation with pretreatmentefficacy evaluation, much water in feedstock presented a buffering effect on reaction and transfer issuesduring steam explosion process, thereby weakening the actual severity of treatment. 40% water contentof cellulosic biomass was optimized from the compromise between treatment efficacy and energy effi-ciency. The yield of overall glucose through pretreatment and enzymatic hydrolysis was increased byover 20% with a potential cost savings of steam consumption by simply coordinating water content ofcellulosic biomass prior to steam explosion treatment. Thus, results in the work emphasize the watertransfer and regulation during steam explosion process on understanding water reaction mechanism,enhancing pretreatment efficacy and saving energy, leading to more efficient use of biomass.