Abstract: By the data of earthquake cases with 58 Ms≥5 earthquakes in mainland China, this paper has studied the relative relation between the earthquake anomaly continuing effective time and lasting time in detail and presented the calculating formula of earthquake anomaly predicting effective timd (that is, the best estimating value of earthquake anomaly continuing effective time) by earthquake anomaly lasting time. Through inspection of many kinds of mathematical statistical methods, the formula has been proved to be reliable and avaiable, which established the foundation to further more develop the study of earthquake anomaly precursory information magnitude and also provided quantitative analysis basis for usually determining the problem of earthquake anomaly continuing effectiveness in daily seismological consideration. So this study might has real significances.