Abstract: The paper analy zed the coefficient of va riation(C_V) and earthquake intero ccurence time before the 6 strong earthquakes along North-south ea rthquake belt in China. The result shows that sev eral mo nths or one year before the main-shock, the coefficient of variation drops slowly, ranging from 0.5~1.3. Among six strong earthquakes, the variation of C_V drops in long and medium term before four earthquakes. The result indicates the coefficient of C_V reflect some complexity of seismic precurso rsbefore strong earthquakes.

Key words: Coefficient of variation, Strong earthquake, Seismicity, Earthquake prediction