In order to compare the effects of different drying pretreatments(CO2 supercritical drying, freeze drying and conventional drying) on pore structure of poplar tension wood, deformations of specimens before and after drying as well as nitrogen adsorption isotherms were measured, which would be expected to provide a theoretical basis for the quantitative characterization of micro-pore structure of tension wood. The results showed that poplar tension wood under CO2 supercritical drying had intact mesoporosity(pore size 2-50 nm). BET specific surface area and mesopore volumn were much higher than those of samples under freeze drying and conventional drying. Freeze drying and conventional drying could cause significant shrinkage deformations of specimens in longitudinal and tangential directions, while CO2 supercritical drying could retain the porous texture quite intact by avoiding the pore collapse phenomenon induced by interface tension. CO2 supercritical drying is suggested to be the best drying pretreatment to characterize the pore structure of tension wood.