A data transmission method and apparatus are provided. The method comprises: receiving service data sent by a first terminal, the first terminal being a single-mode terminal or a multi-mode terminal; monitoring forwarding load traffic of a back-end egress of a first network device in a first network; when the load traffic reaches present load traffic, switching a current forwarding mode to a routing mode, and selecting a second terminal as a forwarding node of the first terminal, the second terminal being a multi-mode terminal; forwarding the service data to the second terminal, so that the second terminal coverts the service data and sends the converted service data to a second network device in a second network. According the embodiments of the present invention, the technical problem of a low utilization rate of the total bandwidth of a network egress in the prior art is solved.