Large scale molten salt storage tanks are widely used in the solar thermal power systems. For these tanks, buckling is a primary failure mode because of its features such as large scale, thinned wall and high temperature. Suffering high temperature condition is a major distinction between molten salt storage tanks and other water or oil tanks. High temperature can cause large thermal deformation for large scale structures which may have an effect on the safety assessment, especially on buckling assessment. Meanwhile, the hydrostatic pressure of molten salt can also cause the change of tank’s configuration. In this paper, a typical large molten salt storage tank has been studied. The critical buckling loads of the tank roof are obtained using nonlinear buckling analysis considering thermal loads and hydrostatic pressure. The results are discussed and some conclusions are proposed for engineering design.