5. The method according to claim 1 , wherein the first message carries a first code word, the first code word is allocated to the application user identity by a first ProSe entity, and the first ProSe entity is a ProSe entity in an HPLMN of the first terminal; and wherein acquiring, by the receiving ProSe entity, the application user identity comprises: acquiring, by the receiving ProSe entity, the application user identity according to the first code word.
5. The method according to claim 1 , wherein the first message carries a first code word, the first code word is allocated to the application user identity by a first ProSe entity, and the first ProSe entity is a ProSe entity in an HPLMN of the first terminal; and wherein acquiring, by the receiving ProSe entity, the application user identity comprises: acquiring, by the receiving ProSe entity, the application user identity according to the first code word. 7. The method according to claim 5 , before the sending a second message to the monitoring terminal, further comprising: sending, by the receiving ProSe entity, a code message to the first ProSe entity, wherein the code message carries a first identity, a first application identity, and a fourth identity, the first identity is a temporary terminal identity that is allocated to the first terminal by the first ProSe entity, the first application identity is an application identity of the first application, the fourth identity is a temporary application user identity that is allocated to a second application user by the first application server, and the second application user is a user of the first application of the monitoring terminal.