The integral equation (IE) method is commonly used to model time-harmonic electromagnetic (EM) phenomena. One of the major challenges in its application arises in the solution of the resulting ill-conditioned matrix equation. Here, we introduce a new domain decomposition (DD) based iterative method for the IE solution of time-harmonic electromagnetic problems. There are two major ingredients in the proposed IEDDM: (a) the method is a type of non-overlapping DD method and provides a computationally efficient and effect preconditioner for the dense matrix equation from the IE method. (b) The presented method is very suitable for dealing with multi-scale EM problem. Each sub-domain has its own characteristics length and will be meshed independently from others. Numerical results demonstrate superior performance of the IE-DDM.