The invention discloses a network number coordination method of multiple networks in a power line network. In the condition that the root nodes of multiple networks can not communicate, a network number is configured automatically, and the engineering efficiency is greatly improved. The method comprises the steps of (1) carrying out conflict detection on the network number of a local network, (2) reporting conflict information to a root node by a leaf node when the leaf node judges that an adjacent network with the same network number exists near the leaf node, (3) judging whether the conflict information in the step (2) has the unique identification of an adjacent network root node or not, executing the step (4) if so, and executing the step (5) is not, (4) comparing the unique identifications of the two root nodes of the local network and the adjacent network, and changing the network number according to a specified rule, and (5) carrying out randomly backoff for a period, and if the leaf node of the local network reports conflict information after the backoff is ended, changing the network number of the local network immediately. The invention also provides a system.