Abstract: his paper uses radon concentration measurements on the profile of active fault to assess the position, scope and activity of faults in Chengdu Region. It can be found that Wenchuan Earthquake affected faults strongly. The radon concentrations were monitored on profiles of Beichuan Fault, Pengguan Fault and Xinjin-Pujiang Fault. The results indicate that the background radon concentration on the profile of active faults is higher than other places. The closer r to the epicenter, the higher the value of radon concentration on the profile of active faults. By data processing, the ratios of radon anomaly threshold value to background value of radon concentration are no more than three and the ratios of maximum radon concentration to background value of radon concentration are less than five. Considering the geological conditions of measurement location such as the topography and surface soil structure, the activities of active faults in Chengdu region are evaluated after the earthquake. There is no fault with high level of activity in Chengdu region. Moreover, the activity of Beichuan Fault and Xinjin-Pujiang Fault is higher than that of Pengguan Fault.