A data processing method includes: inserting multiple alignment markers (AMs) into a first data stream, where the first data stream is a data stream that is transcoded and scrambled after being encoded at a physical layer; adaptively allocating the first data stream that includes the multiple AMs to multiple physical coding sublayer (PCS) lanes to obtain second data streams; performing forward error correction (FEC) encoding on the second data streams on the multiple PCS lanes to obtain third data streams; and delivering the third data streams to multiple physical medium attachment (PMA) sublayer lanes according to an input bit width of a serializer/deserializer (SerDes) to obtain multiple fourth data streams, each fourth data stream includes at least one complete and continuous AM, and the at least one AM is an AM in the multiple AMs.