Sealed structure of plant biomass resists assault on cellulose from enzymatic deconstruction. In this study, pretreatments of triploid poplar were conducted with 0.5 wt % H2SO4 at various temperatures (100-200 degrees C) to loosen the intricate structure. The effect of temperature on cellulose structure and enzymatic digestibility was evaluated. The results indicated that the effective removal of hemicelluloses and amorphous cellulose incurred the increment of crystalline indices of residues. Companied with the degradation of carbohydrates, inhibitory compounds were accumulated with the increasing severity. On the whole, 120 degrees C was considered as the optimum temperature by taking the balance between substrate digestibility and recovery into account.