The spatial distribution and activity characteristics of Shimian fault, an important part of the Daliangshan fault zone, have great theoretical significance for the study of regional tectonic stability, and also have important application value for urban construction and risk assessment in this area. Combined with the data of geological survey, previous trenches, and shallow artificial earthquakes, a comprehensive analysis was made through the geochemical exploration of fault gas radon along the Shimian buried fault, and the results show that: (1) The spatial location of the fault revealed by fault gas radon detection is in good agreement with that interpreted by geophysical exploration and trenches. The fault is located near the peak concentration and is distributed in the abnormal range of the main peak. (2) The tendency of Shimian buried fault determined by fault gas radon detection is consistent with the results revealed by geophysical exploration and trenches. According to the comprehensive data analysis, the occurrence of the fault is N38°-45°W/SW∠70°-80°. (3) The relative activity of different segments of Shimian fault was judged by using the contrast value of fault gas Rn concentration. It is found that the activity of the southern segment of the fault (Nanya River basin) is stronger than that of the northern segment (Dadu River basin).