The invention discloses a method, in an OLT in a passive optical network, of identifying a long-shining rogue ONU, the method comprising the steps of: A. allocating a specific radio frequency signal at a different frequency to each of ONUs in the passive optical network; and B. when the long-shining rogue ONU is detected in the passive optical network: b1. broadcasting a control message to each of the ONUs; b2. receiving uplink signals in the uplink; b3. recovering the specific radio frequency signals transmitted by the normal ONUs from the uplink signals; and b4. identifying an absent specific radio frequency signal according to the recovered specific radio frequency signals, wherein the ONU corresponding to the absent specific radio frequency signal is the long-shining rogue ONU. The invention further discloses an OLT device performing the method and a method, in an ONU, of assisting the OLT in identifying a long-shining rogue ONU.