A traffic switching method, a device, and a system where, a software-defined networking (SDN) controller acquires a first state of a target gateway, where the target gateway belongs to an SDN gateway group, the SDN gateway group is used to forward traffic that is transmitted between a first network node and a second network node, and multiple forwarding paths on which multiple gateways in the SDN gateway group are located form multiple equal-cost paths between the first network node and the second network node. The SDN controller sends an Address Resolution Protocol (ARP) entry to the target gateway according to the first state, and changes, of the multiple equal-cost paths, a metric value of a forwarding path on which the target gateway is located from an original value to a first value, where the first value is greater than the original value.