In this paper, the Φ3.8×13m centre drive ball mill is studied. After predigested the rotator with its mean characters, the FEM model of the rotator is established. After loading and solving to the rotator with FEM software ANSYS, the former ten modal natural frequencies and vibration modes are got. Through the modal analysis, the position which may be easily destroyed is found. Then the position of the partition board is moved, through the comparative analysis, a good project is carried out. The vibration modes are lessened, most of the vibration amplitudes are reduced, the vibration mode which has huge influence to the structure is avoided, and the dynamic performance of the rotator is improved.