This application discloses a network topology discovery method and a node device. In this application, a root node device sends a link discovery message to a child node device through a first port; receives a link discovery acknowledge message sent by the child node device through a second port of the child node device, where the link discovery acknowledge message includes an identifier of the child node device and an identifier of the second port; and determines a first link based on the link discovery acknowledge message, where the first link is a link between the first port and the second port. According to the solutions of this application, when detecting that a link of a port is connected, the node device discovers an existing topology relationship through message interaction, so as to implement network topology discovery.