A network access method, an interface device, and a mobile network access device are provided. The interface device may specifically include: a first network port, a first processor, and a first universal serial bus (USB) interface, where the first USB interface is connected to the mobile network access device; the first network port is connected to a wired wide area network; and the first processor includes a detection unit and an instruction unit, where the detection unit is configured to detect whether the wired wide area network is available and the instruction unit is configured to send, when the detection unit detects that the wired wide area network is available, first network access instruction information to the mobile network access device by using the first USB interface.