In order to utilize cotton fiber in different industry areas, cotton fiber properties were investigated by using fiber length analyzer, fiber tensile tester, laser confocal microscope and X-ray diffraction, including fiber morphology, mechanical strength, crosssectional area and the crystallinity of single fiber of cotton stalk bast. The results showed that the average length of cotton stalk bast fiber was（1 484.43±753.78）μm and its average width was（18.90±6.61）μm respectively, with aspect ratio was 65.75. It was solid mostly or extremely little hollow, with which was the shape of diamond or circle. The stressstrain curve was highly linear with no obvious yield stage. The elastic modulus of single bast was 13.66 MPa, while the elongation at break and the flexibility of it was 6.32%. The crystallinity of cotton stalk was 21.66%，which indicates that it is easier for the fiber of cotton in absorbing water and other chemicals.