Abstract: The relationship between earthquake swarms and the strong earthquake in North China has been studied, the results show:①Earthquake swarm activity is closely related to regional strong earthquakes, and the frequency of small swarms can reflect the level of regional seismic activity. ②The half year cumulative frequency of M_L ≥ 2.0 swarms great than or equal to 8 can be used as a predictive index of M_S ≥ 5.7 earthquakes. The prediction time is 10 months after the appearance of the anomaly. The value of the predictive efficacy score R is 0.615, greater than that of R0, 0.437, with a 97.5% confidence level. ③Frequency index of earthquake swarms can be tested by Molchan model. For target earthquakes with M_S ≥ 5.0,M_S ≥ 5.5 and M_S ≥ 5.7 respectively, the predicted results are all better than the Poisson model. The prediction probability gain can be achieved 2~4 for the 60% of the target earthquakes especially. ④The place prediction of earthquake swarms to the strong earthquake is limited. Two years before the Zhangbei M_S6.2, Ruichang M_S5.7 and Qianguo M_S5.8 earthquake, swarms are mainly active in the vicinity of the tectonic zones associated with the strong earthquake. While they migrate to the epicenter and the surrounding area 2 months to 10 months before the strong earthquake. But for the rest strong earthquakes, the place prediction of swarms is not significant.