A port auto-negotiation method and a device used for implementing port auto-negotiation between high-speed Ethernet devices are provided. The method performed by a first device includes: configuring a first port of the first device as four subports, where each of the four subports includes a differential transceiver channel; determining from the four subports, at least one subport whose differential transceiver channel operates normally, and selecting some or all of the at least one subport as a normal subport; sending capability information of the first port to a second device by using the normal subport, and receiving, by using the normal subport, capability information of a second port of the second device; and determining operating statuses of the four subports based on the capability information of the first port and of the second port.