Abstract: Several materials, such as pure titanium, 304L stainless steel and aluminum, have been chosen to model buckling and post-buckling behaviors of spherical-cone metallic diaphragms for positive expulsion tanks during reversal with different angles (8°~12°), which involve material nonlinearity and geometric nonlinearity. The tangential stiffness of structure will be zero while pressure loaded on the metallic diaphragms increases to the critical load during reversal;however, the Newton-Raphson method could not track the post-buckling equilibrium configuration. The problem has been solved by arc length method. Numerical results by finite element method demonstrate that angle takes the most significant effect on expulsion behavior of 304L stainless steel diaphragm, followed by pure titanium and aluminum. Buckling load and load-carrying capacity during post-buckling equilibrium configuration increase along with smaller angle. The optimum angle is 10°, which takes internal volume and expulsion efficiency of diaphragms into consideration.