Abstract: A method of semi-random and semi-algebraic structure was presented for constructing the low-density parity-check matrix that corresponds to the information bits of the IRA codes. Compared with the existing structural LDPC codes, the distinct advantage of the presented compact structural array for information-bit-corresponding matrix is that the position coordinate of each 1 element in this matrix can be calculated by a determinate algebraic expression, which not only reduces the consumption of memory resource for the random parity-check matrix, but also provides the potential probability for designing low complexity hardware circuit of the LDPC encoder/decoder. In addition, compared with the existing practical LDPC codes in industrial standard, the presented IRA-LDPC code is also slight preponderance in the performance of simulation in bit error rate and signal noise ratio (BER-SNB).