An automatic expansion method, a management device, and a management system are disclosed in the embodiments of the present invention. In the embodiments of the present invention, information about added management nodes is received from a node management server when a new node is added, where the information about the added management nodes comprises at least address information of the added management nodes; the address information of the added management nodes is used to obtain an index corresponding to a continuous identifier (ID) segment; and an adding message of the new node is sent to all added management nodes, where the adding message includes at least a continuous ID segment managed by the new node and address information of the new node.