Abstract: From the exponential distribution function, more deep going discussion has been made on the synthetical anomaly index based on many kinds of seismic precursory anomalies. Synthetical anomaly index has direct mathematical origin and contains clear physical meaning. The loss ef ficiency in loss ef fect distribution functio n has given values according to divided sections and related to the states of some predict ion means or methods in earthquake study.That is, it has given the anomaly degree of some prediction means or methods in certain study time. Loss effect of the product means that anomaly appears in the prediction means o r methods and the anomaly index has been got.After the anomaly index is weighted, the single anomaly index has been got.Having synthesized anomaly index, thesynthetical anomalt index has been got. Finally, it is used in Ningxia earthquake monitoring region and the prediction test is made.It has been found that the synthet ical anomaly index is better correlated with 9 moderately strong earthquake events occurred in Ningxia and its neighboring region.

Key words: Synthetical anomalyindex, Exponential distribution, Earthquake precursor