Chemical constituents in different parts of cotton bast fiber were studied. The different degumming methods for cotton bast fiber, such as retting, degumming with normal pressure, and degumming with high pressure were investigated, and the chemical constituents of degummed cotton bast fiber were also discussed in this work. The experimental results demonstrated that after high pressure degumming, the contents of hemi-cellulose and lignin of the cotton bast fiber have reduced obviously. The content of cellulose is increased. Length and fineness of cotton bast fiber after different degumming methods were measured. The morphology and structure of degummed cotton bast fiber were examined by SEM, FTIR and WAXD analysis. Meanwhile, the stress and strain of the degummed fibers were also tested, and rupture curve was shown. Then, on the basis of the experimental data, a better degumming method was determined.