Abstract: This paper deals with the variations of parameters of geomagnetic characteristic line at the reference geomagnetic stations which are close to some epicenters of strong earthquakes, 45 strong earthquakes(31 earthquakes of M=5 and 14 of M≥6) occurred in the last twenty odd years are refered and the parameters including k, the slop of the characteristic, and c, the correlation coefficient, as well as r, the standard error, are used in this paper. Geenrally speaking, the parameters vary within critical v lllue(k, -0.16, c: 0.75, r: 1.8)but in two or three months prior to earthquakes, there seems to have variations in k, c and r, exceeding the critical values mentioned above, and the variations show a so-called coupled anomaly, i. e. an increase in c and a decrease in k. One of the obvious advantages by using the parameters combination in prediction is that the percentage of false forecast has been decreased. Besides the internal symbol test is better, the actual result in trial prediction of earthquakes has been achieved.