A method for ensuring media stream security in an IP Multimedia Subsystem network is disclosed. The method includes: assigning an end-to-end media stream security key for a calling User Equipment (UE) or a called UE, by a network device with which the calling UE or the called UE is registered, respectively, and transmitting the media stream security key to a network device with which the opposite end is registered; encrypting the end-to-end media stream security key using a session key shared with the calling UE or the called UE respectively, and transmitting the encrypted end-to-end media stream security key to the calling UE or the called UE, respectively, via a session message; encrypting or decrypting a media stream, by the calling UE or the called UE, respectively, using the end-to-end media stream security key.