A further hydration test was conducted to study the influences of curing regime, hydration temperature of water, water–cement ratio on moisture migration of ultra-high-performance concrete (UHPC) matrix. The mechanism for water transport and consumption under further hydration was analyzed, combined with the changes of combined water content for further hydration, microscopic appearance, and pore structure. The results show that the combined water content of UHPC matrix showed a tendency of decreasing with the increase in specimen depth, when the further hydration time was same. During the further hydration process, the longer the curing time of high-temperature water soaking, the higher the hydration temperature of water, the larger the water–cement ratio, the larger the combined water content of UHPC matrix. The combined water content for further hydration displayed a tendency of increasing with the increase in further hydration time. During the early period of further hydration, the combined water content for further hydration displayed a tendency of decreasing with the increase in curing time of high-temperature water soaking, but its value increased sharply during the late period of further hydration. During the further hydration process, the higher the hydration temperature of water, the larger the combined water content for further hydration. The combined water content for further hydration decreased first and then increased with the increase in water–cement ratio, when water–cement ratio ranged from 0.18 to 0.30. High temperature function accelerated the further hydration of cement, and the new further hydration products continuously filled the internal pores and initial defects of UHPC matrix, and the pore structure was refined, and further hydration was manifested as filling effect. However, when the hydration temperature of water (60℃) was too high, microcracks were generated inside UHPC matrix, and the pore structure was coarsened, and further hydration was manifested as damage effect. Research results provides experimental and theoretical bases for the application and life-cycle design of high-performance concrete and ultra-high-performance concrete structures over long service periods in water environments.