Using the self-consistent mean field theory, we have studied the self-assembly behavior of AB/CD block copolymers blend. Simulation results show that the hierarchical structural transitions from lamellar structures on different spatial scales to core-shell structure were caused by the increase of the fusion degree between components B and D. When the mutual fusion degrees between components B and D, between A and B, and between C and D are equal, the structure will change from macro-lamellar to micro-lamellar. In addition, the variation of free energy with the interaction between B and D were also calculated to deepen the understanding about the structural transition.