Abstract: The change in intensity, scope and component of radon released from faults can be used to analyze and evaluate the relative activity of active fault. The basic feature of main active faults in Tianshui area is analyzed. And the radon content is surveyed, the result shows that the activity of west Qinling fault is strong to extremely strong,the activity of Lixian-luojiabu fault is strong,the activity of Lixian-jishixia fault is strong to middle,the activity of west Qingshui fault is middle. The survey results accord with its activity intensity, so radon surveying can be regarded as a method for fault activity evaluation.