Zeolite was utilized to partially or completely (0%, 50%, 100%, volume fraction) replace river sand and the effect of zeolite on the macro and micro properties of seawater mixing ultra-high performance concrete (UHPC) was studied. The flowability, setting time, autogenous shrinkage and compressive strength of UHPC were tested. Besides, the water absorption and water releasing of zeolite as well as the interfacial transition zone (ITZ) of UHPC were studied by low field NMR and nano-indentation. The results reveal that seawater mixing enhances the hydration of UHPC, so it shortens the setting time, increases the compressive strength and the autogenous shrinkage of UHPC. However, zeolite absorbs chloride ions, which inhibits the accelerated hydration induced by chloride ions, extends the setting time of UHPC and reduces the compressive strength. In addition, the internal curing effect of zeolite effectively improves the autogenous shrinkage of seawater mixing UHPC, and its optimization effect is better than that in freshwater mixing UHPC. The phenomenon can be attributed to the earlier and longer releasing water time of zeolite in seawater mixing UHPC. As the strength of porous zeolite is lower than that of river sand, the early compressive strength of seawater mixing UHPC gradually decreases with the increase of zeolite content. After curing 28 d, because the internal curing effect of zeolite optimizes the interfacial transition zone, the later hardening paste is further compacted.