For large SDN networks, the placement and application of multiple controllers is in urgent need. A multi-controller placement approach based on bat algorithm was proposed, and three indexes were optimized, which minimized the average control delay and the controller's load difference, and remove the isolated nodes. The minimization of average control delay was realized when the average control was continuously optimized during one iteration, and the load balance was guaranteed by limiting the load utilization of the controller. At the same time, the tag delivery algorithm was used to remove the isolated nodes to ensure the intra-domain communication. The simulation results show that this approach can guarantee that SDN network achieves small delay and load balanced multi-controller placement without isolated nodes.