A convolutional LDPC decoding method for a serial decoder architecture, wherein the method comprises: receiving, by a decoding unit, first check node information comprising all check node information that is corresponding to a target bit and output by a previous-level decoding unit; reading, by the decoding unit, from a symbol caching unit, a symbol value corresponding to the target bit; determining, by the decoding unit, a log-likelihood ratio, LLR, and a first a posteriori probability, APP, based on the first check node information and the symbol value, wherein the first APP is used to indicate a decoding result of the target bit at a first moment; and sending, by the decoding unit, the first check node information and the first APP to a next-level decoding unit, so that the next-level decoding unit obtains a second APP and second check node information based on the first check node information and the first APP, wherein the second APP is used to indicate a decoding result of the target bit at a second moment, and the second check node information comprises all check node information that is corresponding to the target bit and output by the next-level decoding unit, wherein the determining the LLR and the first APP based on the first check node information and the symbol value comprises: determining extrinsic information of each bit corresponding to the symbol value, wherein the symbol value corresponds to at least two bits and the extrinsic information is a sum of all check node information output by the previous-level decoding unit; determining the LLR based on the extrinsic information of each bit; and determining that a sum of extrinsic information of the target bit and the LLR is the first APP. receiving, by a decoding unit, first check node information comprising all check node information that is corresponding to a target bit and output by a previous-level decoding unit; reading, by the decoding unit, from a symbol caching unit, a symbol value corresponding to the target bit; determining, by the decoding unit, a log-likelihood ratio, LLR, and a first a posteriori probability, APP, based on the first check node information and the symbol value, wherein the first APP is used to indicate a decoding result of the target bit at a first moment; and sending, by the decoding unit, the first check node information and the first APP to a next-level decoding unit, so that the next-level decoding unit obtains a second APP and second check node information based on the first check node information and the first APP, wherein the second APP is used to indicate a decoding result of the target bit at a second moment, and the second check node information comprises all check node information that is corresponding to the target bit and output by the next-level decoding unit, wherein the determining the LLR and the first APP based on the first check node information and the symbol value comprises: determining extrinsic information of each bit corresponding to the symbol value, wherein the symbol value corresponds to at least two bits and the extrinsic information is a sum of all check node information output by the previous-level decoding unit; determining the LLR based on the extrinsic information of each bit; and determining that a sum of extrinsic information of the target bit and the LLR is the first APP. determining extrinsic information of each bit corresponding to the symbol value, wherein the symbol value corresponds to at least two bits and the extrinsic information is a sum of all check node information output by the previous-level decoding unit; determining the LLR based on the extrinsic information of each bit; and determining that a sum of extrinsic information of the target bit and the LLR is the first APP.