Method and device for detecting optical network unit, and passive optical network

A method of detecting an optical network unit, ONU, abnormal in a passive optical network, PON, comprising an optical line terminal, OLT, and a plurality of UN comprising abnormal UN, said method characterized by: detecting an identity code of an ONU in an empty window open uplink or empty time slot; where the empty window open uplink is a window in which the OLT does not authorize a bandwidth uplink for any of the plurality of UN; wherein the empty time slot is an opening time between two widths authorized adjacent uplink band, and each of the widths authorized uplink band corresponds to an authorized one of the plurality of UN time; and determine the identity code corresponding to the UN is an abnormal function of identity code UN UN.