Abstract: After analyzing the basic features of stress distribution over tank shell, a stress calculation method is proposed based on the theory of combined cylindrical shells. Compared with the existing modeling methods for stress calculation of bottom by using finite element analysis of tank-soil coupling, a new model which takes foundation settlement as the boundary condition is established. The influence o safe reliability from different structural parameters is studied by using analytical methods of numerical simulated optimization. And elastic-plastic buckling research under quasi-static is carried out by using nonlinear finite element analysis.The results show that new methods and models can significantly improve the accuracy of stress calculation, and part of the achieved results can provide technical data for making standards, which are concerned with large stand cylindrical steel welded oil storage tank.