Cloud platform monitoring system is an important segment to effectively guarantee the quality of cloud services. In this study, the corresponding virtual server monitoring system is designed on the Openstack cloud platform. The system combines the characteristics of Openstack's open source and strong scalability. At the same time, it starts with the bottleneck problem which appears when Neutron, the network component in Openstack faces the huge virtual server traffic forwarding. This study combines SDN technology and openflow, its important southward interface protocol, to solve the traffic bottleneck problem. At the same time, it designs the monitoring system based on Libvirt and sFlow protocol responsible for obtaining data flow of virtual cluster, giving feedbacks of the latest platform load to the upper control module and user, and using control module and flow table to control traffic forwarding. Finally, the whole system platform can achieve load balancing.