In order to improve the impact resistance of large steel tanks, this paper conducts numerical simulation and theoretical analysis research on the impact response of polyurea coated large steel storage tanks. The finite element model of polyurea-coated steel tank is established based on the model developed and validated in previous studies. Numerical results show that external polyurea layers can effectively reduce the local plastic deformation and avoid the perforation damage induced by impact loadings with the angle of 45°. The main mechanism of polyurea coatings are speed reduction and cushion effect. The maximum energy absorption and energy absorption efficiency of the tanks increase with the polyurea layers′ thickness. When the coating thickness is 15 mm, the tank does not be damaged with penetration, meeting the requirements of the British tank design code. According to the tank′s impact response characteristics and the polyurea coating′s mechanism, a theoretical formula for predicting the critical impact velocity is established, which can predict the maximum energy absorption value of the coating tank with a small error, and can be used as a basis for the impact protection design of polyurea coated steel tanks.