Abstract: Ultra-high strength concrete with different mixed fiber doping amounts was prepared by using basalt graded crushed stone, cement, silicon powder and mineral powder as aggregates, 50 mm long steel fiber, 12.8 mm copper-plated microwire short steel fiber and 12 mm polypropylene fiber as reinforcing phases. The effects of the doping amount of mixed fiber on the compressive strength, splitting tensile strength, flexural strength and flexural toughness of ultra-high strength concrete were discussed. The results show that: ①Doped fibers can improve the compressive strength, splitting tensile strength, flexural strength and flexural toughness of concrete samples, and the improvement degree of hybrid fibers on the compressive strength, splitting tensile strength, flexural strength and flexural toughness of concrete samples is better than that of single hybrid fibers and non-doped fibers. ②50 mm long steel fiber significantly improves the splitting tensile strength, flexural strength and flexural toughness of concrete specimens, but the improvement of compressive strength is not obvious. 12.8 mm short steel fiber significantly improves the compressive strength, flexural strength and flexural toughness of concrete specimens, but the improvement of splitting tensile strength is not obvious. 12 mm polypropylene fiber improves the splitting tensile strength and flexural toughness of concrete specimens, but the improvement of tensile strength is not obvious. When the doping amount exceeds 1.35 kg·m⁻³, the compressive strength and flexural strength of concrete specimens will be weakened. ③The optimum doping amount of mixed fiber high strength concrete is 50 mm long steel fiber 35 kg·m⁻³ and 12.8 mm short steel fiber 20 kg·m⁻³.