Abstract: Through different initial preloading stress levels including 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7 applied to concrete, the variation in the effective preloading stress of the concrete at ultralow temperatures was systematically investigated, with a focus on the influence of two typical ultralow temperatures, −80 ℃ and −160 ℃. The experimental results indicate that: the preloading stress loss rate at the cooling points and the temperature uniformity points as well as its preloading stress change ratio at the cooling phase continuously decrease as the initial preloading stress level increases. While its preloading stress change rate at the cooling phase and constant temperature phase as well as its preloading stress change ratio at the constant temperature phase increase first and then decrease. After reaching the cooling point, the preloading stress loss of the prestressed concrete no longer increases but instead decreases at the constant temperature phase, regardless of whether the temperature is higher or lower, and its degree of reduction is related to the applied initial preloading stress levels. The preloading stress loss rate at the cooling points and the temperature uniformity points at a lower ultralow temperature is higher than that at a higher ultralow temperature, but its preloading stress change rate and preloading stress change ratio at the cooling phase and the constant temperature phase behave differently from its preloading stress loss rate. These results and the corresponding fitting formulas provide a reference for the design and risk monitoring of prestressed concrete structures as LNG storage tanks.