In order to ensure the service safety and reliability of composite structures, it is necessary to fully understand the ultimate strength of unidirectional ( UD ) carbon fiber reinforced composites ( CFRP ). In this paper, the distribution characteristics of fiber tensile strength of UD CFRP are studied by considering the strength randomness of single fiber in CFRP and the microscopic heterogeneity distribution of fibers. The finite element simulation model of UD CFRP ultimate strength is established. By comparing with the experimental data, the results show that the finite element model can accurately predict the ultimate strength of UD CFRP. A method to improve the fiber strength distribution was proposed to increase the strength and reduce the dispersion of the composites.