This application provides example data transmission methods and corresponding example devices. One example method includes sending, by a first device, a first packet to a second device, where the first packet includes transmission policy negotiation information, and where the transmission policy negotiation information is used to negotiate a transmission policy used when the second device uses a multipath connection. The first device can then receive a second packet from the second device, where the second packet includes first policy information, and where the first policy information indicates a transmission policy used when the second device uses the multipath connection. The first device can then transmit data with the second device based on the first policy information by using a transmission policy corresponding to the first policy information.