Fluctuation aggravation is a kind of critical phenomenon before suddenly phase cnange. In this paper we discuss premonitory fluctuation aggravation before strong earthquake at this point, such as small earthquake frequency, underground fluid, gas and earth stress and so on. The preliminary conclusions are as followss:
1. Before strong earthquake, the space distribution of small earthquakes which exceed average day active level in a large area is of the orderliness-the active belts of small earthquakes pass through the coming strong earthquake area. The intersecting area of two belts is the site of coming strong earthquake.
2. Before strong earthquake, most of the high frequency day of small earthquakes synchronize the time of the external causes, the external causes that are found at present include syzygy, solar term, magnetic storm exceeding middle level, and atmosphere pressure fall and so on. This kind of high frequency activity of small earthquakes usually appears a month or a day before the coming strong earthquakes.
3. The time of the premonitory fluctuation and the time of small earthquake frequency fluctuation are approximately synchronization, there are relations between them in the cause of formation.
Impending prediction indexes of earthquake as stated here are not only applicable to the many foreshork area, but also to few foreshork area. Because there are many times of premonitory fluctuation before strong earthquake, it is not possible to completely eliminate false for the time prediction of the strong earthquake.