Abstract: The stress analysis of the storage tank's lap-jointed center plates on the elastic foundation under a liquid pressure is presented. Its mechanics model is two lap-jointed semi-infinite elastic-foundation beams. The resulted stress can be used for stress corrosion and fatigue stress corrosion analysis of tank bottom plates. Because the elastic-foundation-beam-coupled-with-rigid-foundation-beam method (type 2) has considered the situation with the annular plate narrow or with the annular plate and the center plate jointed, the stress analysis method of storage tank's center plate is a necessary condition of the above-mentioned method (type 2).