This invention discloses a method for realizing operation of TFO service exempting secondary code-decode of a bridge packet network and a media gateway, in which, the media gateway includes a code-decode unit of the non-TFO state, a TFO signaling test and judgment unit, a TFO transmission unit and a compressed phonetic code-decode unit, when the media gateway loads and transmits the bridge packet net data, if the transmitted data carries with the TFO signaling, which will be transmitted to the opposite end of the packet net for TFO negotiation, if it is successful, then the compressed phonetic code-decode agreed by the two parties are applied to pick up compressed phonetic frames from the forwarded data to be transmitted on the packet network.