Abstract: A further study to a one-dimensional CI transition model is given.The period of the external potential D has a critical value Dc.The phase diagram in the case of D < c is greatly different from that in the case of D > c.When D < c,the phase diagram varies with D and exhibits Farey tree structure in most region of D.When D > c,the phase diagram keeps in the same shape and do not satisfy the Farey tree structure.The procedure of phase transition is studied through the effective potential F(u).

Key words: CI transition, Farey tree, effective potential