The invention discloses a network capacity expansion method and device, relates to the technical field of communication, and is used for accurately expanding the capacity of a network. The method comprises the following steps: determining the current bandwidth condition in a single direction according to an implemented bandwidth and an unimplemented bandwidth in the single direction; performing flow prediction according to the bandwidth current situation and the current flow in the single direction to obtain a flow prediction result in the single direction; obtaining the target port number inthe single direction according to the flow prediction result, the bandwidth current situation and the port granularity; and determining the number of board cards to be expanded according to the totalnumber of the target ports in all the single directions, the number of existing configuration ports, the number of ports to be offline, the number of old ports to be dialed and the number of ports ofa single board card. The embodiment of the invention is applied to network expansion.