A method for realizing non-loss transmission of media stream after switching between the open call and the secret call, the method includes the steps: after the base station receiving the message of switching from the open call to the secret call from the communication terminal, inserting a special media frame in the media stream and transmitting it to the media gateway; the media gateway judging whether checking the special media frame according to the form of the load-bearing of the media stream's incoming and outgoing or the form of the media's coding decoding, whether detect the special media frame or not, the media gateway transmitting the media stream from the incoming to the outgoing. When the special media frame is detected, deciding to transmit directly or run an PCM adaptation process in 64 kbps/56 kbps according to the form of the coding decoding.