Abstract: The paper has studied the seismic sequences of magnitude 6 and above in China from 1966 to 1991 and we have found the seismicity at the early stage (3-7days) follows the following formula:LnS=a-KsT Where S stands for the seismicity, being the function of T; T stands for the time measured by day; a and Ks are constants. Resolve the constant Ks with least square method and differentiate the types of the seismic sequences with it. A sequence with Ks>=0.145 belongs to the type of main earthquake, and a sequence with ks < 0.145 belongs to the type of swarm. Comparing the results with the traditional differentiating results, we have found that about 86 per cent of sequences belong to the same one of the two types in the two ways. This indicates that the Ks may be a better index to differentiate the type of a sequence at the early stage and we can use it to predict the seismic tendency after a strong shock.