Efficiency pursuit of the distribution system operation should be on the premise of security. This study proposes the network reconfiguration (NR) approach comprehensively considering N−1 security and network loss. A new approach called distribution system security region (DSSR) is first applied in NR problem. The DSSR is the feasible operation space of a system within N−1 security criterion and can quantify the N−1 security margin. Then, the NR is formulated by using the minimum network loss as objective function and the N−1 security margin, which is provided by the DSSR, as constraints. Moreover, the security margin constraints can be customised for each feeder individually, yielding proper compromises between security-related and efficient concerns. Different NR results for multiple security and efficiency requirements are presented on an extended IEEE-RBTS test system. Compared with the traditional minimum-loss NR, the proposed approach reduces the network loss as much as possible with desired security margin, well balancing the security and efficiency of NR.