In order to determine whether the increase of gas radon concentrations at the monitoring point of the Jiayuguan fault since June 2015 can reflect the stronger activity of the Jiayuguan fault or not, the authors applied the cross-fault measurement method based on the typical distribution pattern of soil gas across faults and analyzed comprehensively the relationship between the abnormal changes of gas radon concentrations and the fault activity through multi-component correlation analyzing and theoretical modeling. The results show that the concentrations of CO₂, CH₄, and H₂ from the same monitoring point do not increase during the rapid increase of the gas radon concentrations from the monitoring point of the fault. There is no positive correlation between them. The adding of gas radon concentration does not come from deep crust and it does not mean the stronger activity of the Jiayuguan fault. The results of the gas radon measurement across faults which lie on both sides of the monitoring point show that the gas radon concentrations are different, and this is consistent with the typical distribution pattern of fault gas on the unchanged side of the surface environment but it does not conform to the typical distribution pattern of fault gas on the changed side of the surface environment. The increase of gas radon concentrations is correspondingly with the change of the surface environment in time. Therefore, the increase of gas radon concentration at the fault monitoring point is caused by the change of the surface environment, and the activity of the Jiayuguan fault does not increase. This method provides a thinking for the improvement of reliability in using fault soil gas to judge fault activity.