Disclosed is method for scheduling a data message in a Passive Optical Network (PON) and Ethernet Over Cable (EOC) networking, which may include: an Optical Coax Unit (OCU) allocating a coaxial side Logical Link Identifier (LLID) for a Coaxial Network Unit (CNU) which accessed the OCU, and acquiring an optical network side LLID allocated for the OCU by an Optical Line Terminal (OLT); and establishing a mapping relationship between the coaxial side LLID and the optical network side LLID, and scheduling a data message of the CNU according to the mapping relationship. Also disclosed are a system for scheduling a data message in a PON and EOC networking and a related device. By means of the technical solution provided in the embodiments of the present disclosure, an optical network side of the OCU is effectively separated from a coaxial side thereof, the OLT in an existing PON will not be influenced, an existing Multi-Point Control Protocol (MPCP) will not be modified, and effective control and allocation for resources are implemented.