A Passive Optical Network (PON) multicast management method includes: an Optical Line Terminal (OLT) performs multicast control according to multicast control information, and generates a corresponding multicast downstream command; the OLT sends the multicast downstream command to an Optical Network Unit (ONU); and the ONU resolves the multicast downstream command, and performs multicast control according to the multicast downstream command. Accordingly, a PON multicast communication system, an OLT, and an ONU are disclosed. Through the multicast control mechanism introduced into the PON system, the PON multicast functions are enhanced, and the same data destined for multiple ONUs is prevented from being sent repeatedly in the network, and thus the network bandwidth resources are saved.