Abstract: The tensile creep behavior of ultrahigh performance concrete (UHPC) under loading conditions at very-early-age is a critical factor influencing its early-age stress state and deformation control. Due to significant differences in its microstructure compared to conventional concrete, its response mechanism to sustained loading is more complex. By introducing a damage variable D to construct the effective stress expression, the difference between the actual stress and the effective stress is reflected. Basis on this, the existing ZC creep model is modified to establish a constitutive relationship that can describe the coupling effect of damage and creep. Through systematic tensile creep tests on UHPC under different loading ages and stress levels, the influences mechanism of effective stress evolution on creep development were analyzed. The results showed that the creep of very early ages increases with age later and gradually decreases after 4 d of aging. The higher effective stresses are induced due to early damage development under the same nominal loading stress, thereby promoting creep progression. It indicates that the effective stress is one of the dominant factors influencing creep behavior. After 3 d of aging, the microstructure of UHPC stabilizes, and the time-dependent rate of the damage parameter D relative to the effective stress \boldsymbol\sigma '\left(\boldsymbolt\right) decreases significantly. The ZC model being modified by effective stress can more accurately predict the tensile creep behavior of UHPC at very-early ages, and the intrinsic relationship between damage evolution and creep development during loading being revealed. It can be as a reliable theoretical basis for the early-age performance evaluation and crack control of UHPC structures.