Large-scale virtual computing system requires a loosely coupled virtual resource management platform that provides the flexibility to add or subtract physical resources and the Convenience to upgrade the platform and so on. Openstack provides large-scale virtualization solution such as "Cells" and "Tricircle/ Trio2o ". But because of the complexity, it’s difficult to be deployed and maintain for small cloud computing teams. We discuss a loosely coupled cloud cluster infrastructure. It is based on the database and plug-in to achieve information collection, virtual machine scheduling and controlling and uses a simplified method to achieve unified management of network and images. It can flexibly expand or reduce cluster members, deploys different versions of Openstack and even heterogeneous cloud platform. We will show and analysis this infrastructure. The test bed works well in IHEP.