Abstract: There is no formula and regulations available for design of wall thickness-variable bottom of vertical conicalbottom tank. In this background, based on the stress calculation formula of the rotary thin-walled shell and the no bending moment theory, the design formula of conical-bottom thickness has been deduced under the hydraulic pressure. The finite element numerical calculation results show that the conical-bottom tank has a serious stress concentration at the joint of the conical bottom and the wall (large angle seam). Analogy is made with spherical tank, with curved generatrix rotary thin shell to replace original straight generatrix rotary thin shell, and its thickness calculation formula is deduced. Taking the 3 200 m³ vertical conical-bottom tank as an example, two conical-bottom structure models are established using the finite element software ANSYS, and their calculation results are compared. The results show that the stress and deformation of the arc plate conical-bottom tank are much smaller than that of straight plate conical-bottom tank, and the stress concentration at large angle joint mitigates significantly. Moreover, the numerical calculation is made for arc plate conical-bottom tanks with different plate lengths to identify the relationship between the arc plate length and the stress and deformation.