High-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)Ce2O7 (HECO) was synthesized as a potential thermal barrier material. The hot corrosion behavior of HECO in the mixture of V2O5 + Na2SO4 with variable aggressiveness was investigated from reaction crystallization kinetics, as well as La2Ce2O7 (LCO). Overall, HECO exhibits smaller corrosion depth than LCO except for partial exfoliation. Sluggish diffusion effect of HECO greatly inhibits nucleation of corrosion products, while a horizontal growth is triggered along (001) crystal plane, leading to a reduction in corrosion depth. Meanwhile, with the aggressiveness of molten slat strengthened, reaction kinetics is accelerated and arouses a sharp alleviation of corrosion.