Abstract: This paper focused on the problem that the code-based physical layer security coding has a large security gap. Firstly，this study proofed that the smaller the channel fading amplitude of the confidential information nodes is, the lower the bit error rate becomes in low-density parity-check codes. Then the confidential information nodes were hidden where the legitimate channel amplitudes are minimum, which turned the decoding condition better for legitimate receiver. Finally the scrambling was used to spread the error to the whole code words, which increased Eve’s error probability. The simulation results show that the security gap of this method is reduced by 23.5dB and 4.5dB compared with direct transfer and scrambling, respectively.