Abstract: This paper numerically analyzes the effects of elastic modulus, yield stress and elongation percentage on the post-buckling of spherical-cone diaphragms for positive expulsion tanks based on orthogonal tests. With orthogonal tests, the number of tests is greatly reduced, without affecting the validity of results. Numerical results are as follows: according to the specific diaphragm considered in the paper, its elastic modulus and yield stress have a marked effect on its post-buckling, while the elongation percentage hardly affects the post-bucking of the structure. The top node displacement of diaphragms increases with the increase of the elastic modulus and the decrease of the yield stress. As a result, large elastic modulus, small yield stress and about 20% of elongation will be optimal for diaphragm expulsion.