A new approach is developed for calculating the dynamic response of multi-spool rotor systems with several intershaft bearings using the combined methodologies of the finite element method (FEM), transfer matrices (TM) and impedance methods. The approach makes use of FEM to model shaft elements and then transforms the system properties to transfer matrix mode. The intershaft bearings are treated by the impedance method. It combines the advantages of these three methods. Some numerical examples are considered to check the viability of the method.