A method for authenticating an optical network unit, an optical line terminal, and an optical network unit are disclosed. An ONU is not allowed to be migrated in an authorized manner to an OLT of another vendor for use, so as to bind the ONU and a vendor. An embodiment of the present invention includes: when an optical network unit ONU goes online, obtaining, by an optical line terminal OLT, first vendor information of the ONU, where the first vendor information is vendor information of a vendor to which the ONU belongs; comparing, by the OLT, the first vendor information with second vendor information, where the second vendor information is vendor information of a vendor to which the OLT belongs; and if a comparison result indicates that the OLT and the ONU belong to different vendors, determining, by the OLT, that authentication on the ONU fails.
