On the basis of microearthquake data recorded by the Datong telemetry network, the temporal and spatial evolution regularity of small earthquake swarms in the region is analyzed by using the combination pattern theory. The results show that the predicted epicenter is consistent with the real epicenter of the Datong-Yanggao M_S 5.8 earthquake occurring on Oct. 18, 1989. In addition, through the analysis on relation of earthquake swarms to external causes, the origin time is predicted better.