Abstract Ultra-high performance concrete (UHPC) has been applied widely in modern structure construction. The outstanding mechanical properties of UHPC not only enable strong yet slim structural designs but also highlight its potential in protective structural constructions against extreme loads. In this study, the shear transfer behaviors of UHPC are investigated by push-off tests on Z-shaped specimens, investigating the influences of the microsteel fiber volume ratio and stirrup reinforcement ratio on the shear strength, shear slip, and shear crack width of UHPC. The test results indicate that using a microsteel fiber can enhance the shear strength of UHPC specimens. Within a reasonable range of the steel fiber volume ratio (optimum volume ratio ranges from 0% to 2.5% for microsteel fiber), the shear strength and shear slip of UHPC increase significantly, and the shear crack width reduces with an increasing steel fiber volume ratio. Additionally, the ductility, shear strength, and shear slip of UHPC increase significantly, and the shear crack width reduces with increasing stirrup ratio. Finally, the simplified empirical equations for the ultimate shear strengths of UHPC specimens are deduced, and indicate good agreement with the experimental results.