Logistic chaotic sequence is an encryption sequence, which enhances the security of the information sequence. At first, low density parity check (LDPC) channel coding is applied to logistic chaotic sequence. The chaos sequence is generated randomly, and the watermark is scrambled with the sequence. And then, LDPC coding modulation is applied to the watermark message which is embedded to discrete cosine transform (DCT) domain of the host image. At end, double encryption is realized. Thus, the capacity of resisting disturbance during information transmitting process is advanced, the error rate is reduced and the stability of the transmitting system is increased.