The present invention discloses a multimedia conference system and method that enables peer-to-peer communication between private network and the Internet. The multimedia conference system and method that enables direct peer-to-peer communication between private network and the Internet includes: a plurality of user agents (to receive call requests) constituting a local network; a calling terminal positioned outside the local network and connected to the local network via Internet; a network address translation (NAT) positioned on the gate of the local network as barrier between the calling terminal and the user agent, and a SIP Proxy Server positioned between the calling terminal and private network and logically installed in parallel with said NAT to receive session initiation protocol messages transmitted from the calling terminal, connect, and transmit IP addresses, so as to send the message to specific User Agent(s).