Abstract: In practice， earthquakes typically involve a mainshock followed by a series of aftershocks， and their occurrence is highly unpredictable. The mainshock damages the structure， and the aftershocks worsen the response and damage of the structure. However， no studies have investigated the effects of stochastic seismic sequences on AP1000 nuclear power plants. This paper proposes an analytical framework for studying the dynamic response and reliability of AP1000 nuclear power plants under stochastic main aftershocks. Stochastic main aftershock sequences are generated using the physical stochastic function model of ground motions， narrow-band harmonic group superposition method， and Copula function. The dynamic response of the AP1000 nuclear power plant is analyzed by using ABAQUS software. The direct probability integration method （DPIM） is used to obtain the probability density function of the maximum displacement response in the horizontal direction of the shielded building， and its dynamic reliability is calculated. The results show that the acceleration and relative displacement of the top of the shielded building and the steel containment vessel have increased to varying degrees after the aftershock， compared with experiencing the mainshock only. Additionally， the damage area between the water tanks and the vents has expanded. The aftershocks could cause further damage to the nuclear power plant. The dynamic response of nuclear power plants exhibits a high degree of randomness due to the stochastic ground motions. Aftershocks can reduce the reliability of nuclear power plants to varying degrees under different thresholds.