In the design of electric motors, especially in humanoid robots, early design choices have a significant impact on the end result, especially in terms of vibration and noise, which directly affects the performance of the product. The usual practice is to meet the dynamic performance output of the motor through experience design, and then calculate the vibration noise of the motor, which lacks a simple and reliable analysis method to evaluate the vibration and noise level of permanent magnet synchronous motor. In this paper, a simple and effective dynamic model is established based on Euler Bernoulli beam theory, and the relationship between structural parameters and vibration level is summarized by studying its wave propagation characteristics and vibration response under electromagnetic excitation. The accuracy of the model and calculation method is verified by comparison with the data in the literature. The proposed model is not to completely replace the complicated and fine finite element analysis, but to quickly understand the vibration of the product at the initial stage of design, which provides a new idea for the design and optimization of the motor.