Anomalous annual variation of well water has higher prediction efficiency in moderately strong earthquakes，but factors such as rainfall，groundwater exploitation can also cause dynamic change of water levels． In this paper，the method of dynamic annual period is used to identify anomalous annual variation of water level in Changli well，from 2000 to 2013． The result shows that anomalous annual variations in 2012 and 2013 are related to earthquake precursory anomaly，the anomalous annual variations in other times are mainly caused by rainfall， well observation condition changes，or groundwater exploitation． This shows anomalous annual variation can be the basis for earthquake situation judgment．