In an interleave division multiple access （IDMA） system, different interleavers are used for different users, and all the users employ a common spreading sequence to spread the spectrum. Hence, interleaver plays a key role in the IDMA secure communication. As there are no interleaver designs for IDMA secure communications, this paper proposes a design scheme of an asymmetric IDMA interleaver based on the discrete Arnold map, which implements the secure communication via the method similar to the asymmetric encryption scheme. Simulated results show that the proposed interleaver is of the performance as good as that of the pseudo random interleaver, and that it is effective in performing secure communications.