Abstract: Many hydrogeochemical elements in Shiliquan Well (△=60km) showed synchronous abnormalchanges before Cangshan Ms 5. 2 earthquake. On the basis of the changes, we have researched the characteristics and forming mechanism of them and considered that the synchronous abnormal changes of many hydrogeochemical elaments increeased the reliability of seismic anomalies and that the abnormal extent of water Hg content is larger and clearear than other hydrogeochemical elements. We have obtained the conclusion that the synchronous abnormal change of many hydrogeochemical elements in Shiliquan Well is the reflection of stress increasing caused by activity of Cangshan-Nishan fault zone near the well before Cangshan Ms5. 2 earthquake, which contains the information of the activity ofsource fault.