In the report, the main composites of two species of wood common Chinafir (Cunninghamia lanceolata) and poplar "Sanbei" No.1(Populus nigraP.simonii) were processed with acetylation and the changes of chemical group and the stability of chemical structure of main composites of wood in the process were investigated. The results showed: during the process of acetylation, new nonpolar chemical functional group was found in all the lignin, cellulose and hemicellulose isolated from the wood and the amount of OH group was decreased; under the same process condition, the degree of acetylation of cellulose was lower; meanwhile, during acetylation process hemicellulose was easier to be decomposed, but the lignin and cellulose were more stable. Thus, the acetylation was a useful method of wood surface nonpolarization.