A method and system for negotiating interface data path establishment is provided in the invention, including: making a decision, by Target ASN-GW, on whether to establish an R4 data path or an redirect R3 data path, and sending a corresponding request to the Anchor ASN-GW according to the decision; and determining a negotiation result, by the Anchor ASN-GW, according to the corresponding request from the Target ASN-GW, or the corresponding request from the Target ASN-GW and a local decision, and returning a reply to the Target ASN-GW according to the negotiation result. In this way, the R3 data path is redirected if either the Target ASN-GW or the Anchor ASN-GW determines to redirect the R3 data path; and an R4 data path is established only if both the Target ASN-GW and the Anchor ASN-GW determine to establish the R4 data path.