A method, a device, and a network system of establishing a tunnel are provided in embodiments of the present disclosure. The method of establishing the tunnel includes: obtaining, by a WTP, an address of an AC and an address of a BRAS from a DHCP server; using, by the WTP, the address of the AC to establish a CAPWAP control tunnel with the AC; and using, by the WTP, the address of the BRAS to establish a CAPWAP data tunnel with the BRAS. By using the technical scheme provided in the embodiments of the present disclosure, the CAPWAP data tunnel may be established between the WTP and the BRAS.