Abstract: The secondary surveillance radar(SSR) is an important equipment for air traffic control(ATC). In order to ensure flight safety, SSR signal should be protected without interference by effective methods. This paper briefly introduces the main functions of SSR, puts forward a simulation caculation of SSR monitoring staion, and gives the calculation formulae and calculation conditions. According to the analysis and configuration of the technical parameters for ground SSR, airborne SSR and ground based SSR radio monitoring station, the results of ground based monitoring station distance are given in this paper.