A method for transmitting delay media information in an IP multimedia subsystem, comprising: a sending party of media information sending key generating parameters which are at least partly encrypted to a mailbox server of a receiving party of the media information, and the mailbox server storing the key generating parameters which are at least partly encrypted and sending the key generating parameters which are at least partly encrypted to a key management server, KMS; the KMS decrypting, with a shared key Ka, parameter(s), which is encrypted with the Ka, in the key generating parameters which are at least partly encrypted and which are sent by the mailbox server, to acquire all the key generating parameters, generating a media key Ke2e and an integrity transmission key Ke2m by using all the key generating parameters acquired, sending the Ke2e and the Ke2m to the sending party, and sending the Ke2m to the mailbox server, wherein the Ka is the shared key between the sending party and the KMS; the sending party sending media information encrypted with the Ke2e to the mailbox server by using the Ke2m; the receiving party acquiring from the mailbox server the key generating parameters which are at least partly encrypted, and sending to the KMS the key generating parameters which are at least partly encrypted; the KMS decrypting, with the Ka, parameter(s), which is encrypted with the Ka, in the key generating parameters which are at least partly encrypted and which are sent by the receiving party, to acquire all the key generating parameters, generating the Ke2e by using all the key generating parameters acquired, and sending the generated Ke2e to the receiving party; and the receiving party acquiring from the mailbox server the media information which is encrypted with the Ke2e by the sending party, and decrypting the acquired media information with the Ke2e. a sending party of media information sending key generating parameters which are at least partly encrypted to a mailbox server of a receiving party of the media information, and the mailbox server storing the key generating parameters which are at least partly encrypted and sending the key generating parameters which are at least partly encrypted to a key management server, KMS; the KMS decrypting, with a shared key Ka, parameter(s), which is encrypted with the Ka, in the key generating parameters which are at least partly encrypted and which are sent by the mailbox server, to acquire all the key generating parameters, generating a media key Ke2e and an integrity transmission key Ke2m by using all the key generating parameters acquired, sending the Ke2e and the Ke2m to the sending party, and sending the Ke2m to the mailbox server, wherein the Ka is the shared key between the sending party and the KMS; the sending party sending media information encrypted with the Ke2e to the mailbox server by using the Ke2m; the receiving party acquiring from the mailbox server the key generating parameters which are at least partly encrypted, and sending to the KMS the key generating parameters which are at least partly encrypted; the KMS decrypting, with the Ka, parameter(s), which is encrypted with the Ka, in the key generating parameters which are at least partly encrypted and which are sent by the receiving party, to acquire all the key generating parameters, generating the Ke2e by using all the key generating parameters acquired, and sending the generated Ke2e to the receiving party; and the receiving party acquiring from the mailbox server the media information which is encrypted with the Ke2e by the sending party, and decrypting the acquired media information with the Ke2e.