Based on the correlation between the temporal variability coefficient of seismic activity before strong earthquakes and the b-value, the relative characteristics of space and time of 40 strong earthquake cases (M>6.5) are discussed in this paper. The analysis indicated that the correlation coefficient curve has the stage feature, which is caused by the b-value being deviated in the relative temporal stage with stress field variation. Next, the three elements of future strong earthquakes were estimated using the feature of the first stage of the correlation process, and some empirical formulas for predicting time and magnitude are given. Finally, the reliability of the first stage of the correlation process is discussed. The research results of this study were not apparent for small and moderate earthquakes.