Abstract: In order to investigate the properties of uniaxial tension and mechanism of strengthening and toughening of ultra-high performance concrete containing coarse aggregate, the method of uniaxial tension is used to study the toughness of uniaxial tension; the method of X-ray computed tomography and image analysis introducing fiber dispersion coefficient and fiber orientation factor, is used to study the true distribution of steel fiber in ultra-high performance concrete. It illustrates the relationship between steel fiber distribution and coarse aggregate, steel fiber distribution and uniaxial tensile toughness. The experimental results reveal that steel fibers take coarse aggregate as the center, surround distributing, coarse aggregate having adverse effects on the steel fiber distribution, the more of coarse aggregate content, the larger of particle size, the poorer of fiber dispersion, the lower of uniaxial tension toughness. Steel fiber distribution is closely related to uniaxial tensile strength and toughness of ultra-high performance concrete. With increasing of fiber dispersion coefficient and the orientation factor, uniaxial tensile strength, toughness index and tension and compression ratio are increased, the toughness of concrete reinforced.