A novel approach of constructing time-invariant LDPC convolutional codes is proposed. The matrix of an LDPC (Low-Density Parity-Check) convolutional code with a given rate is generated according to the original matrix generated by Tanner etc. Then

the matrix with maximum given encoding memory and fast encoding property is obtained by modifying the above-mentioned matrix. The fast encoding property of the proposed matrix can reduce the encoding complexity. And the maximum given encoding memory of the proposed LDPC convolutional code can improve the decoding performance. The characteristic parameters and simulation results show that the proposed LDPC convolutional codes are excellent .