The invention relates to an IPv6 (Internet Protocol Version 6) address allocation method, which comprises the steps of: carrying out network parameter negotiation based on an NCP (NetWare Core Protocol) option when terminal-side equipment initiates a PPP (Point-to-point Protocol) connection request to a network side; carrying out interface identification configuration option negotiation by the terminal-side equipment by sending a first configuration request message to a BRAS (Broadband Remote Access Server) during the negotiation process; and carrying out IPv6 prefix negotiation between the terminal-side equipment and the BRAS through at least a configuration request massage after completing interface ID (Identification) negotiation, and realizing automatic address configuration according to a negotiation result fed back by the BRAS and an IPv6 address generated by the interface identification which are received by the terminal-side equipment. The invention further relates to an IPv6 address allocation system. According to the embodiment of the invention, the IPv6 prefix negotiation is completed through the network parameter negotiation of the NCP option in the PPP connection, the automatic address configuration is realized, the configuration complexity is simplified, the network operation and maintenance costs are reduced, and bridging-type and routing-type home gateway scenes can be simultaneously met during the negotiation process.