As the emergence of cloud computing, millions of corporations and organizations had put their service on cloud. In this topic, we need re-implement Bench4Q tool as a service (BaaS) deploying on the application server (JOnAS). BaaS should support elasticity and multi-tenancy which are promised in cloud computing. The tenants of BaaS are supposed to deliver the address of system under test and descriptions of the stress testing to BaaS, and then receive reports on system under test after testing without concerning about managing and coordinating the testing resource beneath the cloud computing platform.