Dynamic behaviors of a rotor with a transverse fatigue surface crack have been studied a lot in the past. In the present study the rotor containing a transverse crack with semi-elliptical fronted edge is considered since the crack grows in an elliptical path when the rotor is subjected to long time cyclic loads through fatigue experiments and realistic cases. Using the finite element method, the stiffness of the shaft with the semi-elliptical fronted transverse crack is calculated. Then, the vibration responses and the coupling mechanism of bending and torsional vibrations of the rotor with and without torsional excitation are analyzed. The result shows that there are slight differences between the dynamic responses of the straight fronted cracked rotor and the semi-elliptical fronted rotor in common frequency fields and high frequency fields. The similar contrast is obtained when the rotor system is applied by torsional excitation.