The nonlinear consistent equations were put forward which could describe beam-wave interaction in an relativistic backward wave oscillator(RBWO), using the nonlinear theory of RBWO. The nonlinear consistent equations were solved by numerical computation, some basic rules of superradiation caused by a non-stationary beam-wave interaction were opened out in an RBWO. Some relations and discriminations were presented between superradiation and stimulated radiation in an RBWO.