The study found that strong magnetic anomalies repeatedly took place before big earthquakes. Based on geomagnetic record analysis results, we discussed a possible pattern of the magnetic anomalies prior to earthquake. In meizoseismal area or epicenter, in a time period of 36 h to about 10 min before earthquake, the exceptional big geomagnetic change increases with the magnitude of earthquake. We calculated that, in a place of 1 km from the epicenter, the magnetic anomaly before destructive earthquakes of Ms 6 - 9 can reach to 10^2 - 10^4 nT（the magnitude of earth magnetic field is 104 nT）, rather than the magnitude of 10 nT from seismomagnetic effect theories since 1960s. From this we speculated the abnormal magnetic ULF near epicenter before earthquake seems to be an ＂intermittent magnetic eruption＂. Accordingly, we proposed that geomagnetic induction earthquake alarm can be a new pre-warning method to surmount hardship in solving the puzzledom of earthquake imminent prediction.