1. A network address translation traversal system for real-time communications, comprising: a user terminal equipment located in a private network; a network address translation device; an IMS located in a public network, being configured to instruct the network address translation device to create a network address translation mapping for a real-time communication connection; and a peer terminal located in the public network, being configured to create the real-time communication connection with the user terminal equipment via the network address translation device directly according to the network address translation mapping; wherein: the user terminal equipment is configured to transmit a first invitation message, the first invitation message comprises a first session initiation protocol parameter corresponding to a session initiation protocol, a first session description protocol parameter corresponding to a session description protocol, and a first Internet protocol parameter corresponding to an Internet protocol and a user datagram protocol, and the first session initiation protocol parameter, the first session description protocol parameter and the first Internet protocol parameter each comprise an Internet protocol address and a port number; the network address translation device is configured to receive the first invitation message and translate the first invitation message into a second invitation message, and in the second invitation message, the first Internet protocol parameter is translated into a second Internet protocol parameter; the IMS is configured to receive the second invitation message, and according to a comparison between the first session initiation protocol parameter and the second Internet protocol parameter, instruct the network address translation device to create the network address translation mapping for the first session description protocol parameter and a second session description protocol parameter and translate the second invitation message into a third invitation message, and in the third invitation message, the first session description protocol parameter is translated into the second session description protocol parameter; and the peer terminal is configured to receive the third invitation message, and create the real-time communication connection with the user terminal equipment via the network address translation device directly according to the third invitation message.