Cement， fly ash and silica fume were used as raw materials， and modified Andreasen-Andersen（MAA） model was used to guide the mix design of the ultra-high performance concrete （UHPC）. The work performance， compressive strength， apparent density and hydration product characteristics of UHPC under different mix proportions， water-binder ratios and curing methods were studied. The residual sum of squares （RSS） was used as an index of the stacking density， and the characteristics of hydration products and compressive strength of UHPC was analyzed to prove the rationality of MAA model guiding UHPC mix design. The results show that silica fume was beneficial to improve the stacking density of UHPC. When the RSS of UHPC reaches the minimum of 570.64， the compressive strength of UHPC under standard curing and steam curing reaches the maximum of 140.4， 153.9 MPa， indicating that the mix proportion design of UHPC by MAA model has high accuracy. Through the research of UHPC hydration products， it is found that the hydration reaction is not complete. High water-binder ratio and high cement content can promote the hydration reaction. The reaction of fly ash and silica fume in an alkaline environment consumes calcium hydroxide to form calcium silicate hydrate （C-S-H） gel. The system Ca/Si mole ratio is reduced， the microstructure of UHPC is improved， and the density and strength of UHPC are improved.