The distributed structure of agents makes the test for large and complex Web service composition possible. This paper discusses how to develop the multi-agent test environment for BPEL-based Web Service composition. The BPEL-based Web Service composition is modeled by HPN that can be easily referenced by test case generation and test evaluation. By representing agent in HPN, the agent can be dynamically bound at runtime. In order to implement the multi-agent test environment for BPEL-based Web Service composition, the ontology is analyzed and defined based on XML because of its flexibility, extensibility etc. This ontology is the basis of the agent communication and provides the terms for test case generation and test evaluation etc. The test case generation and test evaluation under this test environment are analyzed. The test process is provided to illustrate the inter-action between the agents under this multi-agent test environment to accomplish test task.