Embodiments of this application disclose a decoding method, so as to improve FEC decoding performance and a system transmission capability. The method according to the embodiments of this application includes: receiving, by a receive end device, a first bit signal; performing, by the receive end device, level-M forward error correction FEC decoding on the first bit signal to obtain a second bit signal, where M is a positive integer greater than zero; checking, by the receive end device, the second bit signal to obtain a first check resu performing, by the receive end device, level-(M+1) FEC decoding on the second bit signal based on the first check result to obtain a third bit signal; and performing, by the receive end device when M+1 reaches a first preset threshold, data processing on the third bit signal to obtain a fourth bit signal, where the fourth bit signal is used by the receive end device to obtain service data transmitted by a transmit end device.
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