In order to explore the mechanical behavior of dome of a large LNG storage tank under accidental impact loading, the dome local shell of a 16×10⁴m³LNG storage tank was taken as the original model to be tested, the impact resistant design code was used as a reference, impact tests of 15 working conditions were conducted by changing thickness of shell, mass of a flying projectile and its impact velocity. The test results showed that under accidental impact loading, pit damage appears on the dome local shell facing bullet surface, but there is no crack along radial and circumferential directions, the steel plate and concrete at the back have different damage types; projectile body energy, intrusion attitude, and reinforcing bar resistant force have great influences on concrete pit, penetration depth and steel plate failure modes; when the projectile kinetic energy is the same as that of the impact resistant design code and the projectile falls in the gap between reinforcing bars, the steel plat at the dome local shell back is not destroyed, but the concrete at the back has a crack or a circular cap flaking zone, pay attention to this situation during design and safety assessment. Based on the test data, an empirical formula was fitted for estimating the dome failure of a large LNG storage tank under accidental impact load.