Abstract The soil radon (Rn) concentration of the Macheng-Tuanfeng fault has been measured through radon measurement. A comparison of the measuring results and regional geological section leads to discussions of the geographical location, scale and occurrence of the Macheng-Tuanfeng fault. The result reveals that the major fault generally strikes NNE across the Fuzihe town and Yanjiahe town, dipping north and with a high dip angle, and the width of fracture zone ranges from tens of meters up to one hundred meters. Combined with the measured data and the available soil radon appraisal methods of fault activity, we consider that the Macheng-Tuanfeng fault still has a high level of activity. The data also indicates a soil radon anomaly with an imbalance between south and north; we supposed this for two reasons: 1) the activity of the Macheng-Tuanfeng fault presents a weakening tendency from north to south; 2) due to the Macheng magnitude 6.0 earthquake, the release rate of radon gas has increased near the earthquake area.