Security and stability control systems ensure the secure operation of power systems. Existing function tests of stability control systems are typically performed in offline environment using centralized open-loop testing

which cannot effectively address complex dynamic conditions and suffers from limitations in real-time performance and adaptability. To overcome these shortcomings

this paper presents a distributed online testing method based on hardware-in-the-loop

enabling online testing with non-real-time simulation tools. First

key technologies such as synchronization

information exchange

and result evaluation in a distributed system are studied. Then

an event identification algorithm suitable for dynamic testing is designed according to testing requirements. Next

a multi-round closed-loop iteration testing platform is developed to provide comprehensive testing results and verify the effectiveness of the stability control systems. Finally

a pilot application of the proposed method is conducted on the stability control system of a sending-end power grid. Simulation tests and engineering validation confirm the performance of the proposed testing method.