Optical network unit and registration method and system thereof

Disclosed are an optical network unit (ONU) and a registration method and system thereof. The method comprises: an ONU exchanging channel information with an optical line terminal (OLT) on any sub-channel, and obtaining a sub-channel allocated to the ONU itself; and the ONU performing registration and communication on the sub-channel allocated to the ONU itself. In the present invention, an ONU exchanges channel information with an OLT on any sub-channel, so under a situation that sharing of a plurality of SPs exists in a next generation passive optical network, the ONU registers on a correct OLT and completes sub-channel allocation.