The magnets and vacuum chambers, which are the main facilities of the Pohang light source are installed on the storage-ring girders. System safety and reliability should be taken into account for the precise operating of the main facilities, so vibration analysis is essential to do this. Static and seismic analyses were performed for the design of structure considering safety, and also frequency and response spectrum analyses were performed for the precise alignment. With these results, the effects of surrounding vibration were checked. This paper explains about the design and vibration analysis of girder systems.