A method for transmitting a multicast preview service, characterized by comprising: an Optical Line Terminal, OLT, configuring a management object and/or attributes of the management object in an Optical Network Unit, ONU, wherein the management object and/or the attributes of the management object comprises at least one of the following: Multicast Operations Profile, MOP, an authorization group of Extension Multicast Operations Profile, EMOP, an Allowed preview groups table of Multicast Subscriber Control, MSC, and a preview group of EMOP, the step that the OLT configures the management object and/or the attributes of the management object in the ONU comprises:adding a Multicast service package table in an MSC management object, wherein the Multicast service package table comprises a source IP address item, a Virtual Local Area Network Identifier, VID, item and a pointer item which have a mapping relationship with each other, wherein the pointer item records a pointer pointing to an MOP management object instance or a EMOP management object instance; the ONU receiving the multicast joining request message; the ONU looking up, in the management object and/or the attributes of the management object, an attribute carried in a multicast joining request message according to a predetermined sequence, wherein the step of looking up, in the management object and/or the attributes of the management object, the attribute carried in the multicast joining request message according to the predetermined sequence comprises: looking up the attribute carried in the multicast joining request message in the following in turn: the MOP, the authorization group of the EMOP, the Allowed preview groups table of the MSC, and the preview group of the EMOP; forwarding or stopping forwarding to a user a service requested by the multicast joining request message according to a lookup result. an Optical Line Terminal, OLT, configuring a management object and/or attributes of the management object in an Optical Network Unit, ONU, wherein the management object and/or the attributes of the management object comprises at least one of the following: Multicast Operations Profile, MOP, an authorization group of Extension Multicast Operations Profile, EMOP, an Allowed preview groups table of Multicast Subscriber Control, MSC, and a preview group of EMOP, the step that the OLT configures the management object and/or the attributes of the management object in the ONU comprises:adding a Multicast service package table in an MSC management object, wherein the Multicast service package table comprises a source IP address item, a Virtual Local Area Network Identifier, VID, item and a pointer item which have a mapping relationship with each other, wherein the pointer item records a pointer pointing to an MOP management object instance or a EMOP management object instance; the ONU receiving the multicast joining request message; the ONU looking up, in the management object and/or the attributes of the management object, an attribute carried in a multicast joining request message according to a predetermined sequence, wherein the step of looking up, in the management object and/or the attributes of the management object, the attribute carried in the multicast joining request message according to the predetermined sequence comprises: looking up the attribute carried in the multicast joining request message in the following in turn: the MOP, the authorization group of the EMOP, the Allowed preview groups table of the MSC, and the preview group of the EMOP; forwarding or stopping forwarding to a user a service requested by the multicast joining request message according to a lookup result.