A message transmission method, wherein the method comprises: obtaining, by a message processor , message content and an address of an optical network unit ONU; obtaining, by the message processor , a downlink message according to the message content and the address of the ONU, wherein a destination address of the downlink message is the address of the ONU; wherein the address of the ONU is a Media Access Control MAC address of the ONU, and the obtaining, by the message processor , a downlink message according to the message content and the address of the ONU comprises: obtaining, by the message processor , an Ethernet frame according to the message content and the MAC address of the ONU, wherein the Ethernet frame comprises the message content and the MAC address of the ONU, and a destination MAC address of the Ethernet frame is the MAC address of the ONU; or wherein the address of the ONU is an Internet Protocol IP address of the ONU, and the obtaining, by the message processor , a downlink message according to the message content and the address of the ONU comprises: obtaining, by the message processor , an IP data packet according to the message content and the IP address of the ONU, wherein the IP data packet comprises the message content and the IP address of the ONU, and a destination IP address of the IP data packet is the IP address of the ONU; and sending, by the message processor , the downlink message to a relay device by using an OpenFlow message or a preset tunnel, wherein the preset tunnel is a virtual extensible local area networkVXLAN tunnel or a multi-protocol label switching MPLS tunnel. obtaining, by a message processor , message content and an address of an optical network unit ONU; obtaining, by the message processor , a downlink message according to the message content and the address of the ONU, wherein a destination address of the downlink message is the address of the ONU; wherein the address of the ONU is a Media Access Control MAC address of the ONU, and the obtaining, by the message processor , a downlink message according to the message content and the address of the ONU comprises: obtaining, by the message processor , an Ethernet frame according to the message content and the MAC address of the ONU, wherein the Ethernet frame comprises the message content and the MAC address of the ONU, and a destination MAC address of the Ethernet frame is the MAC address of the ONU; or wherein the address of the ONU is an Internet Protocol IP address of the ONU, and the obtaining, by the message processor , a downlink message according to the message content and the address of the ONU comprises: obtaining, by the message processor , an IP data packet according to the message content and the IP address of the ONU, wherein the IP data packet comprises the message content and the IP address of the ONU, and a destination IP address of the IP data packet is the IP address of the ONU; and sending, by the message processor , the downlink message to a relay device by using an OpenFlow message or a preset tunnel, wherein the preset tunnel is a virtual extensible local area networkVXLAN tunnel or a multi-protocol label switching MPLS tunnel. <EOS>