The application of software defined network (SDN) management technology is facing some issues, such as the high payment cost of inter-domain routing and unclear subdomain division of multi-path. Herein, a least-cost payment algorithm based on quality of service (QoS) network assurance and an inter-domain multipath routing control algorithm in SDNs associated with density peaks clustering (DPC) classification has been put forward. By setting QoS network evaluation metrics and introducing the SDN control layer, the network's lowest cost inter-domain multipath routing communication is realized. In addition, two subdomain division evaluation parameters, namely inter-domain separation and intra-domain aggregation are introduced, and the shortcomings of DPC class algorithms are corrected to improve the accuracy of SDN subdomain division and inter-domain multipath control. The experiment results indicate that the network latency of the least-cost payment algorithm is about 60 s in accessing 50 cloud platform service providers, and the cache occupancy rate of cloud platform service providers reaches about 85%, while the network average latency of the inter-domain multipath routing control algorithm is about 11 s, indicating the great potential of SDN management systems in the convergence of satellite communications and 5G communications.