Cluster-based computing systems are very widely used in various fields, including simulations and big data processing. InfiniBand is de-facto interconnect technology for cluster-based computing. QoS is a very important issue in data communication of cluster-based computing systems. In this paper, we propose dynamic QoS scheme for InfiniBand-based clusters. The proposed scheme can change QoS level in terms of the bandwidth. The proposed QoS scheme can get more bandwidth by changing the QoS level. The prototype of the proposed scheme was implemented in a real InfiniBand-based clusters. By using the prototype implemented, we confirmed and evaluated the usefulness and effectiveness of the proposed scheme.