Abstract: The analysis of the seismic response of oil storage tanks has very great significance to the seismic design of such kind of structures.On this article, by applying the theory of velocity potential of fluid flow and theory of elastic deformation of thin shells, the naturalfrequencies and the dynamic responses of the oil storage tanks with small height-diameter ratios supported on the ground which is excited by the horizontal component of an earthquake motion have been analyzed by the finite elements method.The results obtained show that the flexibility of the tank shells can not be underestimated although the height-diamter ratios of the tanks are rather small.