In order to realize the active control of the vibration characteristics of the electric spindle and improve the dynamic performance during its operation，a test platform for the vibration performance of the electric spindle is established by using the electric spindle with adjustable preload. Based on the platform，the experimental study of the vibration characteristics of the electric spindle under different bearing preload conditions is carried out. The results show that：the first-order to fifth-order natural frequencies of the electric spindle system increase with the increasing of the bearing preload，and the second-order natural frequency is most affected by the bearing preload；under the same speed condition， the vibration of the main body of the electric spindle decreases with the increasing of the bearing preload， and the radius of the orbit of shaft centerline also shows a decreasing trend；under the same preload condition，the vibration of the electric spindle increases with the increasing of the rotation speed， but the radius of the orbit of shaft centerline slightly decreases. Furthermore，it is shown that the preload online adjustment technology can effectively control the vibration characteristics of the electric spindle and provide conditions for the development of the intelligent electric spindle technology.