Influence of air flow on sound elimination effect of silencers with double expansion chamber is analyzed by means of the dual reciprocity boundary element method (DRBEM). The results show that the influence of higher Mach number subsonic flow on the sound elimination of complex silencers can not be ignored. Affects of the number of interconnecting tubes, inlet positions and the structural type of diversion annuluses on acoustic transmission loss of the silencers are summarized. Such conclusions are of some practical value for engineering application.