The Songyuan M_S5.7 earthquake occurred on May 28,2018. In order to study the influence of earthquakes on fault gas and the variation characteristics of fault gas after earthquakes,several periods of soil hydrogen observation were carried out in the epicenter after earthquakes. Finally,the maximum and background values of hydrogen concentration in the epicenter region were obtained. Based on the data of hydrogen variation before and after earthquakes,the trend change of hydrogen concentration in epicenter is analyzed. The results show that during this earthquake activity,hydrogen concentration has the phenomenon of "slow increase before earthquakes-decrease when earthquakes are about to occur-sharp increase after earthquakes-a sharp rise again before strong aftershocks". The variation of hydrogen concentration has a good correspondence with seismic activity. Main shocks play a major role in the increase of hydrogen concentration,while aftershocks play an inductive role. Aftershocks release gases trapped in underground rock fissures faster,so aftershocks make hydrogen concentration change more sensitive. In addition,at a certain time after the earthquake,the concentration of hydrogen in the air will also increase,which may be related to the escape of hydrogen from faults to the atmosphere. In addition,at a certain time after the earthquake,the concentration of hydrogen in the air will also increase,which may be related to the escape of hydrogen from faults to the atmosphere. This study shows that hydrogen changes obviously before and after the earthquake,which has very good indicative significance.