The invention discloses a synchronous detection method, which is suitable for a closed-loop system. Data sent by an operation subsystem to an execution subsystem contain sent closed-loop data A1 necessary for normal operation of the closed-loop system and additional sent open-loop data B1, data received by the execution subsystem from the operation subsystem contain received closed-loop data A2 and received open-loop data B2, and the execution subsystem processes the received closed-loop data A2 according to the logic of normal operation and issues to a controlled object, records disturbance of the state quantity and disturbance moment of the controlled object; the execution subsystem records an abnormal phenomenon and abnormal moment of the received open-loop data after processing the received open-loop data B2; and according to the disturbance moment of the controlled object state quantity and abnormal moment of the received open-loop data B2, searching the controlled object state quantity waveform and received open-loop data recording of the corresponding moments. The method is simple to realize, can accurately detect whether synchronization is achieved, and facilitate positioning of a relation between disturbance of the controlled object and synchronization.