Loop-based microgrids are signified by their high reliability in islanded and grid-connected operations. This paper proposes an iterative procedure for the optimal design of a microgrid topology in active distribution networks, which applies graph partitioning, integer programming, and performance index for the optimal design. The proposed approach avoids infeasible and non-optimal designs of microgrid structures and provides remedial solutions for enhancing our previous topology design method. The numerical results for a microgrid test system show that the proposed designated steps can optimize a loop-based microgrid structure in an active distribution network.