Abstract: In this paper, the variational characteristics of the time distribution structure of small earthquakes activity in Shanxi seismic zone before the Datong M6.1 earthquake in 1989 have been studied by muiti-ply fractal theory, It is found that each Dq value showed dimmension-decrease anomaly before the earthquake, and the anomaly of D_+q (q>o) was particularly outstanding. Different earthquake samples are calculated, their anomalous states are basically consistent, which indieates that the inherent structure anomalous variation of time distribution of small earthquakes activity before earthquake is true and reliable. It might be of benifit to our future seismic analysis and prediction studies.