Smart substation technology is rapidly developing and widely used, and the accurate test of relay protection devices is essential. However, for a large number of off-site relay protection devices, the current test mode often lacks flexibility and compatibility, and also cannot display intuitively the test situation to the operator in real time. To address this issue, this paper studies a relay test agent with a coordinated multi-module system architecture based on IEC61850. The agent improves the efficiency and flexibility of tests. Also the test system software ensures the readability of test results. The implementation of relay test agent is given and its advantage in convenience of operation is demonstrated. This work is supported by the Science and Technology Project of State Grid Corporation of China (No. 5229DK18002S).