Cloud computing has emerged as a new paradigm for delivery of computing resources. It has brought great opportunities to performance testing. A four layer model for cloud-based performance testing is proposed. At the same time, an admission control and scheduling algorithm is also designed. All this can achieve the flexible management and dynamic dispatch of shared resources, which are pooled for load generation. The requirements of multi-tenancy can also be implemented. Based on the above mentioned proposition, an available tool, Bench4Q is migrated to the cloud.