Abstract: The characteristics in quietness and activeness for Ms≥5 earthquakes in North China are studied, and a quantitative index for the prediction of over Ms6 earthquake in the area is proposed under the background that the quietness of Ms≥5 earthquake is lasted more than 30 months.Index 1:when the quietness of Ms≥5 earthquakes lasted 30 months in North China, there is the risk of Ms≥6 earthquake;when the quietness of Ms≥5 reaches 40 months, the risk increases further, and the probability of occurrence is 0.54, the R-value is 0.12;when the quietness of Ms≥5 is up to 50 months, the risk probability gets to 0.77 and the R-value is 0.22.Index 2:when the seismic quietness of Ms≥5 in the North China area ends, the risk probability for the occurrence of a Ms≥6 earthquake in 3 months is 0.38 and the R-value is 0.35, the risk probability for the occurrence in 9 months is 0.54 and the R-value is 0.44;the risk probability in 15 months is 0.69 and the R-value is 0.53.