A method and a network device for transmitting a data stream are provided in the embodiments of the present disclosure. The present disclosure relates to the field of communications, can ensure the effective transmission of the data stream, and enhances the quality of service of the network. The method for transmitting a data stream includes: determining, according to a forwarding table, candidate forwarding ports for transmitting the data stream; determining, according to a priority level of the data stream and priority levels of the candidate forwarding ports, forwarding ports for transmitting the data stream; transmitting the data stream through a first forwarding port of the forwarding ports; when the first forwarding port is congested, transmitting the data stream through a second forwarding port of the forwarding ports. The embodiments of the present disclosure can be adopted to transmit the data stream.