Abstract: This paper has produced the physical meaning of the water radon variation rate and the production method of the dynamic pattern of the variation rate.Before strong earthquakes,the dynamic pattern showed high value anomalous areas of vaviation rate 0.06;the maximum variation rate in the center of the anomalous area showed regular evolution with time and showed a good statistical relation to earthquake occurrence time.Based on this,four time preciction indexes have been presented.The testing prediction result showed that the predicted earthquake occurrence time stages mostly lasted from two to six months and could be satisfied with the need of mid short term prediction for strong earthquakes.