Establishing the relationships between intrinsic structure and enzymatic hydrolysis of plant biomass is critical for understanding the process of enzymatic hydrolysis. This manuscript aims to explore the relationships between porous structure and enzymatic hydrolysis by examining the pore size distribution and the parameters of mass transfer in steam exploded corn stover. Results indicated that the pore size distribution and other parameters of porous structure of corn stover were altered by steam explosion pretreatment. These structural changes enhanced the percolation probability and permeability, reduced the threshold pressure, and subsequently improved the enzymatic hydrolysis yield of steam exploded corn stover. Multiple factors regression analysis demonstrated that threshold pressure was a significant factor of enzymatic hydrolysis with a correlation coefficient of 0.885. It revealed that the changes of porous structure could reduce threshold pressure and subsequently improve enzymatic hydrolysis. Based on these results, we have proposed the concept of seepage recalcitrance which provides a key index for pretreatment technology. (C) 2013 Elsevier Ltd. All rights reserved.