Beth turbo codes and LDPC codes can achieve the Shannon limited performance. The constituent RSC codes in turbo codes are more structural and this lends the encoding problem easier with shift_register circuit.While the encoding of LDPC codes is performed via matrix multiplication, it is more complex than it appears for capacity_approaching LDPC codes. On the other hand,the soft_input soft_output BCJR algorithm,or the sub_optimal version of it,used for turbo_decoding is rather complex while sum_product algorithm used for LDPC decoding lends itself to parallel implementation and is computationally simpler. Combining the turbo codes encoding and LDPC decoding,a new scheme based on factor graphs and sum_product algorithm is developed, Which can reduce the decoding complexity of turbo codes greatly,and also has some guides in the designing of interleaver and the choosing of RSC constituent codes. Simulation shows the correctness of the scheme.