A data transmission method for to a data center including a first site and a second site is disclosed. According to the data transmission method, after obtaining a first data packet sent by a virtual machine at the first site, a switch at the first site identifies a service type of the first data packet, and determines routing information of the first data packet based on the service type of the first data packet; and after determining the routing information, the switch sends the first data packet based on the routing information, where the routing information is used to indicate a bearer link for transmitting the first data packet, and a link through which the first data packet is transmitted to the second site is the bearer link. In this way, the first data packet may be transmitted through a link that corresponds to the service type of the first data packet.