Abstract: the character of groundwater level in Sanyuan well before Jingyang Ms4.8 earthquake is discussed, and the emphasis is the variation of tidal response before the event.The analysis on groundwater level indicates that the response ratio of loading and unloading has the feature of smooth-increasing-recovering before the earthquake.The method of response ratio of loading and unloading used in groundwater level tide might catch some precursory information before M5 about earthquakes.