Abstract: This paper mainly discusses the temporal-spatial evolution characteristics of defor-mation anomaly before the Datong earthquakes in 1989, 1991 and the Zhangbei eart hquake in1998. The results show that, if the start time of anomaly is taken as a judgment criterion, thefrequency of deformation anomaly is usually higher than or near twice mean square deviationduring 1~ 2 years before strong earthquakes. That is, this shows the mid-term anomaly of de-formation, which the 3-stages characteristics in the temporal-spatial evolution process are notobvious. If the time of turning point or end time of the deformation anomaly is taken as thejudgment criterion, the frequency of deformation anomaly will come to the maximum value 1~ 4 months before the earthquakes. This shows the short- term information and obvious 3-stages characteristics(a, ß, y). Based on the theoretical analysis of these features, the start-ing time and the time of turning point may be taken as the judgment criterion respectijvely. Ifthe frequencies obtained by two methods are all anomalous, it indicates the anomaly is in thetransitional stage from mid-term to the short-term. Otherwise, it is in the mid-term stage.This analytical idea can be used to judge the transitional stage from mid-term to the short-termof deformation anomaly.

Key words: Deformation anomaly before strong earthquakes, Temporal-spatial evolutioncharacteristics, Starting time of anomaly, The time turning point abnormity