In this paper, the authors have studied the seismic features in the southeast Gansu Province using the mathematic threshold autoregressive model and pisewise polynomial. The results are as follow:
1) The seismicity is of a "periodic phenomenon". There have been 3 cycles since this century. At present, the seismicity is in the third active "period".
2) Since. 1900. the seismicity has been in lower level, most of earthquakes are ones with magnitude of 5-6. The next earthquake will be one with magnitude of about 5 according to the threshold autoregressive model, and its occurring probability at present is 0.74 based on the pise-wise polynomial.
3) The pattern of space distribution of earthquakes (M>4.7) is in accordance with analog-to-digital experiment.