Rotor systems are mostly applied in rotary mechanical devices, which play important roles in aviation, electric power, mechanical and many other industries. These systems usually consist of shafts with multistage impellers, but a series of issues related to strength, fatigue, vibration and noise are needed to be solved. It is in an urgent to improve the performance of such products by optimization method. In rotor system, each impeller contains a blade group that composed of dozens of blades, so the DOF of the entire rotor system is still large, although the rotation period characteristics of bladed disk is used in finite element method. Therefore, the calculating efficiency is still needed to be improved. For this purpose, the single bladed disk can be regarded as a designed subsystem according to aerodynamic performance requirements, and the simplification of the finite element model for the blade group is an effective way to improve the computational efficiency of coupled vibration of bladed disk under the premise of obtaining enough precision. In this paper, an equivalent analysis method is put forward to simplify the blade group into an annular plate with variable parameters based on the criterion that dynamic characteristics can be approximately the same. Physical parameters of annular plate including geometric and material parameters are obtained by theoretical derivation and calculation. Eventually, the equivalent method is verified by taking a bladed disk model of aero engine as an example. It shows that model reduction can ensure the precision with improving computational efficiency. Therefore, the equivalent analysis method is an efficient modeling approach of bladed disk for the future optimization of the whole rotor systems.