Abstract: The previous two papers in this series have proposed a data-diagram model and an initial layout auto-generation algorithm for single-line diagram of substation centralized distribution network（SCDN）, and this paper will focus on beautifying and optimization calculation for the initial layout single-line diagram. The line intersection number of the initial layout single-line diagram has been greatly minimized even to zero, however, the iterative calculation of force-directed algorithm will yield many line intersections caused by the lower class line branches over cross the upper class line sections, therefore, a new force called ‘inertia force’ on the lower class ‘node cluster’ to keep their nodes as a cluster having a certain inertia force to avoid their nodes separating and splitting caused by outside forces. An optimal parameter setting approach for force-directed is provided to minimize the line intersections through optimizing the parameters of different forces consisting of attraction, impulsions between node to node, node to edge and edge to edge, and gravity force, inertia force, etc. Generic algorithm（GA） is used to solve this optimization problem. 10 kV SCDNs of five actual 110 kV substations are testified, the results show that the proposed method can generate a single-line diagram with high identification of connection performance.