The invention relates to a method for changing main machine QoS strategies of a cloud data center. The method comprises that a resource pool business load monitor which is arranged in the cloud data center monitors business load types and load conditions of all physical servers; when the fact that physical servers conform to changing conditions is monitored, proper new resource scheduling algorithms are selected for physical servers; changing commands which inform physical servers of adopting new resource scheduling algorithms are sent to physical servers; after physical servers receive changing commands, existing resource scheduling requests and new resource scheduling requests are sequenced and sectioned, wherein the first section part continues to adopt original resource scheduling algorithms for scheduling implementation, and the second section part adopts new resource scheduling algorithms for scheduling implementation. The invention also relates to a system for changing main machine QoS strategies of the cloud data center. By the aid of the method and the system, the problem of resource allocation caused by diversification of demands in cloud calculation can be effectively solved, and the online changing of QoS strategies can be achieved.