A method to enhance the performance of IDMA system by means of irregular LDPC codes was studied. Interleavers were used as signature character for user identification and iterative turbo detection and decoding approach was employed with reduced complexity. Gaussian approximation was applied to approximate the message probability density function on factor graph with multiple users. Iterative message update formulas on factor graph were derived. Degree profiles were obtained by using the iterative formula. Simulation result shows that the performance of irregular LDPC-Coded LDMA system is better than that of (3,6) regular LDPC-Coded IDMA system in terms of BER and performance gain about 0.6 dB is achieved at BER 10s with 8 users for AWGN multiple access channel.