In this paper, underground radon gas measurement was used in the work to find concealed unusual polarization characteristic faults. The authors employed shallow seismic exploration technology and high-density electrical method to give comparative validation in combination with geological in-situ verification. Analysis shows that the abnormal values obtained from radon measurement can well indicate locations of faults. With the underground radon measurement method, the authors detected the alignment of two other faults in the earthquake area, and made an evaluation of their relative activities. This method overcomes the time-consuming and high cost problem existent in other geophysical methods. In practical work, underground radon measurement provides the reference information for conducting other geophysical methods and implementing projects.