Pretreatment and enzymatic hydrolysis are the two central steps to convert lignocellulosic biomass into fermentable sugars. Here we report a discovery of constant particle size distribution of corn stover and wheat straw in enzymatic hydrolysis after pretreatment. The average particle size of the extensively pretreated corn stover and wheat straw quickly decreases to 20-30 mu m in enzymatic hydrolysis and maintains constant without further size shrinking, although the hydrolysis continues to release glucose. The microstructural properties of the lignocellulose biomass pretreated by different processes and severity during the enzymatic hydrolysis were characterized by the particle size analysis, scanning electron microscopy (SEM) and the polarized light microscopy (PLM). The microstructural analysis reveals that the parenchyma tissue of the pretreated corn stover and wheat straw is quickly hydrolyzed, then the vascular bundle tissue is hydrolyzed to short vascular fibers. The fibers maintain a stable structure by the support of residual lignin framework during enzymatic hydrolysis. A structural model of lignocellulose biomass in pretreatment and enzymatic hydrolysis is proposed based on the pretreatment and hydrolysis experiments, as well as the microstructural analysis. This study takes the first insight into the uniform change of lignocellulose structure during pretreatment and enzymatic hydrolysis with the potentials on elevating hydrolysis yield and reconstruction of cell wall structure.