Abstract: 【Objective】 To provide a chemical pretreatment method which can be combined with fourier transform infrared spectroscopy (FTIR) to observe the cell wall components of cotton fiber.In the method, the cell wall of cotton fiber can be broken without causing structural damage and the real structural components of cell wall can be analyzed by FTIR. 【Method】 Cotton fiber was pretreated with thioglycolic acid and hydrochloric acid, and the free chemical reagent was washed with deionized water.The cell wall of cotton fiber after chemical pretreatment was observed by FTIR.Using the same treatment of the shoots of Pinus sylvestris L.var.mongolica Litv. with high lignification and hardness as control to verify the treatment method. 【Result】 Cotton fiber was broken at the site where it binds to the sulfhydryl group in thioglycolic acid, which could effectively break the cell wall of cotton fiber and overcome the problem that it was difficult to grind the fiber sample. Then the free chemical reagents were washed with deionized water. The cell wall of cotton fiber after chemical pretreatment was observed by FTIR. It was found that the chemically treated cotton fiber was significantly higher than the original chopped cotton fiber in the spectral range of 1,800-1,650 cm^-1. In the spectral range of 1,800-1,550 cm^-1, there was a very significant difference between chemically treated cotton fiber and chopped fiber, in the spectral range of 1,320-1,200 cm^-1, The FTIR absorbance of treated cotton fiber was significantly higher than that of chopped cotton fiber. 【Conclusion】 The cell wall components of cotton fiber can be correctly evaluated by pretreatment of cotton fiber with thioglycolic acid and hydrochloric acid and then combined with FTIR.