Effect of type, length and diameter of steel fibers on the tensile properties of ultra high performance concrete(UHPC) and its pullout behavior were investigated through the uni axial tensile test and single fiber pullout test. It can be explained by scanning electron microscope（SEM） results of fiber surface and interfacial transition zone(ITZ). The results show that the tensile properties and pullout behavior of UHPC with end hooked fiber are better than that of UHPC with straight fiber. Compared to straight fiber, better bonding properties of ITZ between end hooked fiber and matrix contributes to the “yield period” in tensile stress strain curve and platform period of pullout curve. For both type of steel fiber of the same diameter, the elastic tensile strength increases at first and then decreases as fiber length increases. The optimum tensile property and pullout behavior are gained at the length of 16mm. For UHPC with end hooked fibers at the same length, the tensile property and pullout behavior declines, due to increasing parosity and bleeding in ITZ at a large diameter.