This paper presents a novel construction method of irregular Low-density parity-check(LDPC)codes based on Quasi-cyclic(QC) structure and zigzag pattern. By using the proposed method, a class of irregular and highly structured LDPC codes can be designed with the advantages of low storage requirement and linear time encoding complexity. The constructed codes are called Irregular repeat-accumulate like(IRA-like) codes since their parity-check matrices are similar with those of IRA codes,which all contain a sparse zigzag pattern submatrix. The left part of the parity-check matrix of IRA-like codes is a kind of circulant permutation matrix. A best-effort analyzing method for optimizing the cycle structure of IRAlike codes is presented. We further details the proper constraints for avoiding short cycles and low-weight codewords. Simulation results show that the proposed IRA-like codes have low encoding complexity, good iterative decoding performance and flexible choice of code parameters. This paper presents a novel construction method of irregular Low-density parity-check (LDPC) codes based on Quasi-cyclic (QC) structure and zigzag pattern. By using the proposed method, a class of irregular and highly structured LDPC codes can be designed with the advantages of low storage requirement and linear time encoding complexity. The constructed codes are called Irregular repeat-accumulate like (IRA-like) codes since their parity-check matrices are similar to those of IRA codes, which all contain a sparse zigzag pattern The left part of the parity-check matrix of IRA-like codes is a kind of circulant permutation matrix. A best-effort analyzing method for optimizing the cycle structure of IRAlike codes is presented. We further details the proper constraints for avoiding short cycles and low-weight codewords. Simulation results show that the proposed IRA-like codes have low encoding complexity, good iterative decoding performance and flexible choice of code parameters.