The basic mixture of ultra-high performance concrete (UHPC) was optimized by the modified Andreasen & Andersen particle packing model, and the effects of steel fibre shape, content and hybridization on the wet packing density of UHPC were evaluated. Moreover, the D-optimal design (DOD) method was employed for modelling of wet packing density of UHPC against hybrid steel fibres. The results reveal that the incorporation of long straight fibres, short straight fibres and hooked-end fibres have varying degrees of effects on UHPC packing system, among which the end hook fibre reduces the density of UHPC the most. In addition, the steel fibre content has obvious effects on wet packing density of UHPC, and especially as the steel fibre content exceeds 2.0% (volume fraction, below is the same), the packing density of UHPC drops dramatically, resulting in significant damage to UHPC packing system. Based on the analysis results of the DOD model, it is concluded that the hybridization of 0.9% long straight fibres and 1.1% hooked-end fibres is optimized mixture and disturbing effect of steel fibre on UHPC accumulation system is minimized.