The invention discloses an IP multimedia subsystem (IMS) multimedia communication method and system as well as a terminal and an IMS core network, wherein the IMS multimedia communication method comprises the following steps: the terminal carries out signaling negotiation with the IMS core network, and establishes an IPsecurity-encapsulate secure playload (IPSec-ESP) security association for media transmission between the terminal and the IMS core network during the signaling negotiation process and media content transmission is carried out between the terminal and the IMS core network through the IPSec-ESP security association for media transmission. By means of the invention, the safety of the media content transmitted between the terminal and the IMS core network is ensured, the safety problem of multimedia communication under the IMS in the correlation technique is solved, and the multimedia content is prevented from being maliciously stolen and falsified by others when being transmitted between the terminal and the IMS core network.
