Leading pretreatment technologies based on dilute sulfuric acid, liquid hot water, alkali and organosolv were applied to Populus variant. The remaining solids after each pretreatment were hydrolyzed by cellulase to glucose. Mutant poplar exhibited higher accessibility and glucose yield after four different pretreatments. Composition analysis, FTIR-ATR, gel permeation chromatography (GPC) and cross polarization/magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C-NMR) techniques were employed to elucidate structural transformations of poplars during the leading pretreatments. Composition analysis and FTIR-ATR results revealed that hemicellulose and lignin were removed to variant extent during pretreatment. GPC analysis showed that DP of cellulose was decreased the most after dilute acid pretreatment, followed by organosolv, alkali and liquid hot water pretreatment. Cellulose crystallinity index analysed by CP/MAS 13C-NMR indicated that CrI was increased after pretreatment and was comparable between different pretreatment methods. The results also demonstrated that organosolv pretreatment resulted in the most decrease of recalcitrance of poplar to obtain the lowest pretreatment yield and the highest glucose yield in the process of enzymatic hydrolysis. Among the tested properties of poplar, lignin removal during pretreatment and cellulose accessibility were the most important features that associated with glucose release from the Populus.