To deal with the short girth, which caused by the only weight-2 circulant permutation matrices in the current type-Ⅱ quasi-cyclic low-density parity check (QC-LDPC) codes. A method of approximate double diagonal structure of the type-Ⅱ QC-LDPC codes based on perfect cyclic difference families (P-CDF) is proposed. The parity check matrices constructed by this method consist of zero matrices, weight-1 circulant permutation matrices and weight-2 permutation matrices, which not only keeps the girth at least 8, but also retains the advantages of type-Ⅱ QC-LDPC codes with a higher minimum distance upper bound, so that decoding can quickly converge. The simulation results show that the type-ⅡQC-LDPC codes have no obvious error-floor and good iterative decoding performance when decoded by the sum-product algorithm (SPA) under the additive white Gauss noise (AWGN) channel.