A passive optical network, PON, system, wherein the system comprises: an optical line terminal, OLT, and at least two optical network units, ONUs, the OLT is connected to each ONU by using an optical distribution network, ODN, and the OLT and the at least two ONUs exchange data on one downstream channel and two upstream channels; the OLT is configured to send downstream data to each ONU on the downstream channel, wherein the downstream data comprises an upstream bandwidth grant, and the upstream bandwidth grant is used to instruct each ONU to send upstream data; each ONU is configured to receive the downstream data on the downstream channel, and send the upstream data on at least one of the two upstream channels based on the upstream bandwidth grant comprised in the downstream data, wherein the upstream data comprises a registration response packet, first upstream service data or second upstream service data; and the OLT is configured to receive, on the at least one of the two upstream channels, the upstream data sent by each ONU, wherein the two upstream channels comprise a first upstream channel used to transmit the first upstream service data and a second upstream channel used to transmit the registration response packet and transmit the second upstream service data; the upstream bandwidth grant comprises a first upstream bandwidth grant and a second upstream bandwidth grant; the first upstream bandwidth grant is used to instruct an ONU that is in a registered state to send the first upstream service data on the first upstream channel; the second upstream bandwidth grant is used to instruct the ONU that is in a registered state to send the second upstream service data on the second upstream channel or instruct an ONU that is in an unregistered state to send the registration response packet on the second upstream channel. the OLT is configured to send downstream data to each ONU on the downstream channel, wherein the downstream data comprises an upstream bandwidth grant, and the upstream bandwidth grant is used to instruct each ONU to send upstream data; each ONU is configured to receive the downstream data on the downstream channel, and send the upstream data on at least one of the two upstream channels based on the upstream bandwidth grant comprised in the downstream data, wherein the upstream data comprises a registration response packet, first upstream service data or second upstream service data; and the OLT is configured to receive, on the at least one of the two upstream channels, the upstream data sent by each ONU, wherein the two upstream channels comprise a first upstream channel used to transmit the first upstream service data and a second upstream channel used to transmit the registration response packet and transmit the second upstream service data; the upstream bandwidth grant comprises a first upstream bandwidth grant and a second upstream bandwidth grant; the first upstream bandwidth grant is used to instruct an ONU that is in a registered state to send the first upstream service data on the first upstream channel; the second upstream bandwidth grant is used to instruct the ONU that is in a registered state to send the second upstream service data on the second upstream channel or instruct an ONU that is in an unregistered state to send the registration response packet on the second upstream channel.