Background: The electron beam stability is very important for Free Electron Laser (FEL) equipment. The increasing demands of beam position stability result in the higher position stability requirement of the FEL key parts such as undulator and quadruple magnet. Since the mechanical support system for the FEL provides supporting

location and position adjustment

the high mechanical stability of the supports is indirectly expected. Purpose: This work focuses on the research of the dynamic performance of a mechanical support system composed of three dimensional adjustments and a granite block mounted on. It will be applied to the quadrupole in undulator segment for the Soft X-ray FEL (SXFEL) and the Dalian Coherent Light Source (DCLS) project in China. Methods: The Finite-element (FE) calculations of the model characteristics were carried out to guide the subsequent model and vibration experiments. Results: First natural frequency of the support is about 28 Hz. Ratio of the root-mean-square (RMS) displacement (1?100 Hz) between the ground and the top is close to 1. Conclusion: Small RMS ratio illustrates good mechanical stability of the granite adopted by this work. First natural frequency is smaller than the required frequency

which indicates that the further structural optimization is necessary. Abstract