Abstract: The data of wave velocity ratio for more than ten years since 1985 are comparatively studied. It is proposed that i t is necessary to make dynamic analysis of prediction effect. In other words, the time, distance and amplitude of the corresponding earthquakes are changed with the build-up process of strong earthquakes. The anomaly for the short-term and imminent false prediction may provide the long-and medium-term seismogenic information or the focal precursors of the moderately strong earthquakes. The study shows that the moderately strong earthquakes failed to predict are those occurred within a range of 250 km in the following 3 months; and the moderately strong earthquakes, which show the corresponding relation, are those occurred within a rang e of 100 km in the following 5 months. The moderately strong earthquakes occurred beyond the rang e o f 300 km could not be predicted.

Key words: Wave velocity ratio, Prediction effect, Building-upprocess of strong earthquakes, Yunnan Area