An iterative detection/decoding algorithm of correlated sources for the LDPC-based relay systems is presented. The signal from the source-destination(S-D) link is formulated as a highly correlated counterpart from the relay-destination(R-D) link. A special XOR vector is defined using the correlated hard decision information blocks from two decoders and the extrinsic information exchanged between the two decoders is derived by the log-likelihood ratio(LLR) associated with the XOR vector. Such the decoding scheme is different from the traditional turbo-like detection/decoding algorithm, where the extrinsic information is computed by the side information and the soft decoder outputs. Simulations show that the presented algorithm has a slightly better performance than the traditional turbo-like algorithm(Taking the(255,175) EG-LDPC code as an example, it achieves about 0.1 dB performance gains aroundBLER=10~(-4)). Furthermore, the presented algorithm requires fewer computing operations per iteration and has faster convergence rate. For example, the average iteration of the presented algorithm is 33 at SNR=1.8 dB, which is about twice faster than that of the turbo-like algorithm, when decoding the(961,721) QC-LDPC code. Therefore, the presented decoding algorithm of correlated sources provides an alternative decoding solution for the LDPC-based relay systems. An iterative detection / decoding algorithm of correlated sources for the LDPC-based relay systems is presented. The signal from the source-destination (SD) link is formulated as a highly relevant differential from the relay-destination (RD) link. A special XOR vector is defined using the correlated data from defined decoders and the extrinsic information between two decoders is derived by the log-likelihood ratio (LLR) associated with the XOR vector. Such a decoding scheme is different from the traditional turbo- like detection / decoding algorithm, where the extrinsic information is computed by the side information and the soft decoder outputs. Simulations show that the presented algorithm has a slightly better performance than the traditional turbo-like algorithm (Taking the (255,175) EG-LDPC code as an example, it achieves about 0.1 dB performance gains around BLER = 10 ~ (-4)). Furthermore, the presented algorithm requires fewer computing operations per For example, the average iteration of the presented algorithm is 33 at SNR = 1.8 dB, which is about twice faster than that of the turbo-like algorithm, when decoding the (961,721) QC-LDPC code. Therefore, the presented decoding algorithm of correlated sources provides an alternative decoding solution for the LDPC-based relay systems.