In GPS modernization, LDPC code is used in L1C signal to enhance the receivers’ performance in weak signal environments. The LDPC codes used in L1C signal do not have cyclic or quasi-cyclic structure, which increases the complexity of decoder. To reduce the implementation complexity of decoder, the structure of parity check matrix of the LDPC code used in GPS L1C signal was analyzed. Based on the analysis, a complexity- reduced decoder was presented. The presented decoder divides the check nodes into two groups and changes the variable nodes updating way, which can reduce the storage and simplify the control logic of the decoder. The decoding results of the presented decoder are validated by simulation.