In this paper, full-atom models of O2-/CaCl2 were constructed and the systems were described by Born-Mayer-Huggins (BMH) potential function to investigate the dynamic behavior of O2- in CaCl2 molten salt based on molecular simulations. The calculated diffusion coefficient at 1073 K is about 2.01 × 10-5 cm2/s, which is consistent with the reported value of F.D.Ferro"s literature. At the same time, the diffusion coefficient of O2- is closely related to temperatures. When the temperature is increased from 1073 K to 1473 K, the diffusion coefficient is 5.66 × 10-5 cm2/s. The activation energy for diffusion of O2- in CaCl2 molten salt is 15.6 kJ/mol by fitting diffusion coefficients at various temperatures. In terms of the microstructure, Ca2+ can form a positive coordination layer to inhibit the diffusion of O2- due to the electrostatic attraction. Further calculations found that the energy barrier that O2- needs to escape from the Ca2+ coordination layer is about 1.7 J. This article not only reveals the dynamic behaviors of O2- in CaCl2, but also provides guide to research and improvement of molten salt compounds.