Abstract: To make use of methods of the statistical feature and the analog y prediction, some earthquake swarm s and foreshock sequences with typical prediction sense occurred in Liaoning in the past are studied in detail. The results show that there are a lot of obvious differences between foreshock sequence and precursory earthquake swarms. Their nature and precursory characteristics are distinct. The nature and precursory characteristics of pre-seismic sequence of M _S 5. 6 earthquake occurred in Xiuyan-Haicheng in 1999 are similar to that of foreshock sequence of M_S 7. 3 earthquake occurred at Haicheng in 1975, both of them belong to foreshock sequence. Meanwhile, the research results also include the methods for judging of earthquake sequences and the problems necessary to pay attention.

Key words: Precursory earthquake swarm, Foreshock sequence, Nature of earthquake sequence, Precursory characteristics