The embodiments of the application provide a passive optical network planning method and device as well as a passive optical network for achieving maximum coverage of a connected multi-mode terminal node. The method is applied in a network environment with a wireless cellular network, and comprises the steps of: determining that a multi-mode terminal node of a wireless base station is connected tothe network environment; and performing passive optical network planning on a multi-mode terminal node not connected to the wireless base station. The method considers the multi-mode characteristic of terminal nodes, and part of multi-mode terminal nodes of the existing wireless base station provide an access service, so that the deployment cost of the passive optical network is reduced and the coverage of the planned network is improved.