A novel approach to intelligent automatic layout of single-line diagrams for the regional network is presented. The standard substation wiring diagrams are generated by the integration of graph and model technique. The layout area is defined according to the number and configuration of the substations. The layout scheme is formed after completing substation placement and line routing orderly in the layout area. A mathematical model with minimal total line length as the optimization objective is developed. A modified particle swarm optimization algorithm for disturbing inactivated particles and similar particles respectively and randomly is proposed to search for the best layout of single-line diagrams in the fixed routing sequence. Finally， the routing sequence is optimized to further reduce the crossing of lines. The application examples show that the result of intelligent automatic layout is aesthetic and effective for dispatching decision-making.