Data transmission method and device

The invention provides a data transmission method and device, the method is applied to a first network, the first network comprises a second network and a third network, and the method comprises the following steps: a first communication device receives a first message; repackaging the first message to obtain a second message; and sending the second message by using the resource of the first network slice in the third network. Wherein a message header of the first message comprises an identifier of a first network slice, a format of the first message is a message format of a second network, the first network slice is a network slice corresponding to a first service in the first network, and the first message is a message of the first service; the message header of the second message comprises the identifier of the first network slice, the format of the second message is the message format of the third network, and the second message is the message of the first service.