Dear Yulin,
Your images did not show up properly, but your calculation of the tower mass inertia about the tower base looks correct to me.
In addition to the point mass, the rotational inertias of the rotor/nacelle assembly (RNA) play an important roll in the total system inertia. The mass, center-of-mass location, and inertias of the RNA for the NREL 5-MW turbine can be found in my June 1, 2012 post in the forum topic found here: Tower Eigenfrequencies of NREL 5MW Turbine.
Best regards,