Studying vulnerability of storage tanks under the coupling effect of blast wave and fragment can contribute to improve safety level of chemical industrial parks. In the study, the failure limit state equation of chemical tank that subjected to the coupling effect is established based on the energy density rule and maximum plastic strain criterion, which considering the sequential action of blast wave and fragment and the strain-rate effect. Comparative analysis of the theoretical rupture velocity of the storage tank and the maximum speed that obtains by numerical simulation to verify the rationality of the equation. The analysis of the vulnerability of a 5000m3 vertical vault tank shows that the strain-rate effect can enable the tank less destruction of the combined loadings and reduce the vulnerability of the tank. The action sequence of blast wave and fragment significantly affects the failure probability of the tank, while fragment impacts the tank firstly is more dangerous than blast wave. Through a single univariate analysis shows that the vulnerability of the storage tank is positively correlated with explosive strength and impact loading of fragment, but it is negatively related to the impact angle of fragment. The study results are helpful for providing guidance for the prevention of domino effect accident subject to coupling effect of blast wave and fragment and formulating pre-control strategy.