Abstract: The double-floor storage tank can overcome the disadvantages of severe corrosion and strong leakage concealment of the traditional single-floor storage tank, but its upper floor is at the risk of fatigue failure under cyclic loading. Therefore, an axisymmetric model was established based on the structure and load symmetry for the vertical double-floor storage tank with annular grille structure. Through finite element analysis on the fatigue life of storage tanks during long-term service, the distribution of safety factor and fatigue life of the tanks out of service was studied in detail under the conditions of different bottom supports, grille spacing and thickness-to-width ratios of grille. The results show that the tank wall bottom is the most vulnerable part. Under the same grille arrangement and loading, the support mode with the floor connected by angle steel has higher fatigue reliability. Besides, the grille spacing and the thickness-to-width ratio have significant impact on the overall fatigue reliability of storage tanks. With the decrease of grille spacing and the thickness-to-width ratio, the overall safety factor and fatigue life of storage tanks increase, and their fatigue reliability also increases. Generally, the research results could provide a theoretical basis and technical reference for the structural design and optimization of vertical double-floor storage tanks.