This application provides a data reassembly method and an apparatus, to reassemble packet fragments in combination with local reassembly and cloud reassembly, so as to obtain a reassembled packet. This improves reassembly efficiency, reduces a packet reassembly delay, and reduces power consumption of an OLT. The method includes: a first OLT receives a plurality of packet fragments of a first packet that are sent by an optical network unit ONU; and if the first OLT determines that an upload condition is met, the first OLT sends the plurality of packet fragments to a cloud reassembly device, so that after receiving the plurality of packet fragments, the cloud reassembly device reassembles the plurality of packet fragments to obtain a second packet.