The accident procedures are the third level of defense in depth for nuclear power plants, and play a crucial role in limiting the development of accidents and ensuring reactor safety. Accident diagnosis is a key component of accident procedures and the primary prerequisite for identifying the nature of accidents and selecting the best recovery procedures. The completeness, rationality, and effectiveness of the design of accident diagnosis strategies directly affect the effective application of accident procedures, thereby determining the operational safety of power plants. Based on the safety characteristics and accident handling ideas of gas cooled micro reactors, and combined with the task requirements of accident diagnosis, this paper proposes a set of accident diagnosis strategy design methods applicable to gas cooled micro reactor nuclear power plants. The method carries out strategy design from four levels: procedure scope, procedure priority, inlet symptoms, and operation process. By designing the scope of procedures, the integrity of the accident diagnosis strategy is ensured. By prioritizing procedures, a reasonable diagnosis sequence that conforms to the characteristics of gas cooled micro reactor accidents is formulated. The correctness of the accident diagnosis strategy is ensured through inlet symptom design, and the feasibility of the accident diagnosis strategy is ensured through operational process design (Zhang in Research on the Technology of Generating Emergency Procedures for Nuclear Power Plants Based on Symptoms, 2009 [1]). The design method for the accident diagnosis strategy of the gas cooled micro reactor has a complete structure, rigorous logic, precise diagnosis, strong feasibility, and can effectively reduce human errors in accident diagnosis. It improves the accident handling system of the unit under accident conditions, ensures the accuracy and timeliness of accident response, and improves the safety of the power plant.