The minimum break point set(MBPS) is the starting point of complex and ring network setting coordination, which always has so many sets that it needs to select a set of best MBPS. This paper considers the actual utilization for load flow to node and nodes' impact on the vulnerability of breakpoint relay protections, then takes node electric betweenness as measuring indicator of relay's vulnerability and proposes a method for selecting optimum MBPS from many sets of MBPS. Compared with the existing method, the indicator is more in line with flowing characteristics of load flow and actual occupancy for load flow to node, and selected MBPS is more appropriate. Finally, the effectiveness and rationality is proved with an example of simulation.