The automatic generation of the transmission network single-line power flow diagram for dispatching large screen display can be divided into three steps， namely， the single-line diagram layout， the single-line routing， and the real-time data access. The automatic layout of the single-line power flow diagram is studied， which can be decomposed into the supply area layout and substation layout within the supply area to reduce the dimensions of a problem and increase the efficiency for solution. A visual assistance layout tool based on scalable vector graphics（SVG） controlled by Java Script and an automatic layout algorithm are proposed. For the substation layout within the supply area， a compressive objective function is suggested， that is， the intersections should be as few as possible and the distance between substations as short as possible so as to avoid repeated cycles of layout-routing. An automatic layout algorithm based on simulated annealing is provided， by which global optimal solution can be obtained from an initial layout obtained by discretization of the substation geographical coordinates followed by optimization routing. The final dispatching single-line power flow diagram generated after the automatic layout is distinct and with very satisfied effect.