Abstract: In thispaper, the study of synthetical anomalous degree (SAC) was int roduced. The synthetical anomalous degree was synthesized ba sed on precurso ryparameters, methods and the informa tion of observ atio ns from many inst ruments. The result is quite true and credible thatit canbereg ardedas the judg ement to judge the anomalous level of the deforma tion. Furthermore, by analy zing the value of SAD before severalst rong earthquake in No rth and Southw est China regions, welearn tha tabo uthalfyear before the earthquake, the outstanding change of synthetical degree canbe observed (the value of SAD, ranges from 0.1 to 0.3 in usual exceeds 0.5) . Especially in epicent ral regio n and itsvicinity (in the sphere of more than 100 km) , the SAD risesto agreat highvalue (>0.6) . The st ro ng earthquakes alway shappen in the area with SAD exceeding 0.6 in the future. The synthetical anomalous degree can ref lect the level of the precurso ryanomaly and of strong earthquakes; itcan be used to predict the strong earthquakes. But it also needsappro priate dist ributio n and enough density of observation.

Key words: Continuous deformation, Synthetical anomaly, Value of SAD, Precurso rbeforestrong earthquake