Upon annealing Bi1.6Pb0.4Sr2Ca2Cu3Ox compound at 650℃ in flowing oxygen the modulated structure was changed from the Pb-type via the mixed type to the Bi-type. While the specimen was subjected to sequent annealing in flowing nitrogen at 650℃, the modualated structure was changed back from the pure Bi-type via the mixed type to the pure Pb-type. The process was almost reversible. The change in the modulated structure was closely related to the motion of Pb ions. And the inhomogenity of the Pb ion distribution led to the mixed modulated structure.