Continuum phase-field model is adopted to study the phase separation of a binary epilayer grown on the surface of a solid with subsurfacial dislocation array. It is found that there exists interesting competition between the contributions to pattern formation from non-uniform surface stress and the buried dislocations. Numerical simulation demonstrates that various well-ordered composition patterns can be achieved, and their sizes, shapes and spatial orders are controllable in broad ranges. (C) 2003 Elsevier Science B.V. All rights reserved.