The invention provides a multi-agent grid fault diagnosis system and method based on a blackboard model. A task planning Agent of the system divides a multi-agent system; a first information acquisition Agent acquires relay protection information of a power grid in real time, a second information acquisition Agent acquires circuit breaker information of the power grid in real time, and the information is transmitted to a blackboard model sharing platform; the blackboard model sharing platform determines whether the transmission data of the relay protection information and the circuit breaker information are fault data by setting a switching function, updates the received fault data, and obtains the accurate fault data; an information transmission Agent compares and superimposes the received accurate fault data one by one, and obtains the final fault data; a topology Agent determines the topological structure of a fault region; and a fault diagnostic Agent conducts a fault diagnosis to diagnose faulty elements using a Petri network based on the fault data and the topological structure of the fault region.