The access method includes the following steps. Firstly, multimedia data is accessed with a multimedia access device located on a local network, which connected to a public network via a network address translation (NAT) or firewall device. Next, first communication link between a portal server and the multimedia access device is established. Then a piece of punch-through information indicating whether the multimedia access device can punch through the NAT/firewall device is obtained in response to an inquiry command provided by a client device. Next, when the multimedia access device cannot punch through the NAT/firewall device, the multimedia data is pushed from the multimedia access device to the portal server and the multimedia data pushed to the portal server is further pulled from the portal server to the client device, so that multimedia data transmission between the client device and the multimedia access device can be obtained.