Embodiments of the present invention disclose a method, a device, and a system for obtaining a cost between nodes. The method includes: receiving, by a first server, a first cost request message from a client, where the first cost request message includes a first source node list, a first candidate node list, and a cost type; and calculating a cost between each source node in the first source node list and each candidate node in the first candidate node list according to the cost type. Network traffic management and optimization are implemented by using the technical solutions provided in the embodiments of the present invention, in which a cost between nodes is acquired from servers hierarchically deployed by an Internet service provider ISP and used as a basis of node selection.