Abstract: Aiming at the problem of the responsive signal’s identification of airborne mode A/C transponder for civil airport ground receiving station and aviation surveillance system, a method that has a great practical value in the field of civil-aviation application is presented. This method gives the initial results based on the responsive signal’s basic structure that generated by the airborne transponder and the responsive signal’s physical meaning of mode A/C. On the basis of the initial results, some actual situations, such as the responsive signal’s encoding rules of mode A/C for civil airport and aviation route and the flight level that generated by civil aviation of china, are used to identify the responsive signal. Field test results indicate that this paper propose a targeted solution to the responsive signal’s identification of mode A/C. This technique improves accuracy and reliability of the responsive signal’s identification for mode A/C. And it has a great value in civil-aviation surveillance application, such as multilateration.