Abstract: Mechanical test was carried out on the carbon fibre reinforced composite with different thicknesses,and the process of cracking and the mechanic properties were analyzed. The results manifested that for the specimen with the thickness of 1.40 mm,the fibre strands on the fracture were very fine and completely broken indicating that the fibre had been fully strained,the tensile strength of the specimen was 3 050 MPa,elasticity modulus was 156.5 GPa,and ductility was 1.7%,while for the speumen with the thickness of 3.0 mm,the fibre strands were coarse. As there was no strain within the coarse fibre strands,the overall mechanic properties were much low with tensile strength 1847 MPa,elasticity modulus 143.8 GPa,and ductility 1.2%. Compared to the later specimen,tensile strength of the former specimen was enhanced by 65%,elasticity modulus by 8.8%,and ductility by 0.5%.