The workability and mechanical strength of ultra-high performance concrete ( UHPC) are the key to its popularization and application. Therefore, this paper used workability test, rheological test, compressive strength test and flexural strength test to explore the variation of UHPC fluidity, time loss, yield strength, plastic viscosity, compressive strength, and flexural strength under different water reducing agent content and fiber physical parameters. The results show that the fluidity of UHPC increases first and then decreases with the increase of water reducing agent content and fiber content. The time loss of UHPC is mainly related to standing time. The longer the standing time of UHPC is, the greater the time loss is. The rheological curve of UHPC shows a trend of shear thickening. With the increase of water reducing agent, the yield stress and plastic viscosity of UHPC decrease first and then increase, and the minimum value is obtained when the content of water reducing agent is 1. 00% (mass fraction). The effect of water reducing agent on strength is not obvious. The compressive strength of UHPC increases with the increase of fiber content, and the flexural strength increases first and then decreases with the increase of fiber content. When the fiber length is 13. 0 mm, the compressive performance of UHPC is the best, and the flexural performance is the best when the fiber length is 20. 0 mm.