The paper introduces the application of Artificial Intelligence (AI) in medical domain, the medical diagnosis knowledge graph is built based on the 3-layer model of "disease-symptom-feature" through natural language processing, and it dilates upon the intelligent building method and its application in the Clinical Decision Supporting System(CDSS) for the detection of clinical efficacy, the results demonstrate that the medical diagnosis knowledge graph built with the method features high efficiency and high accuracy of disease diagnosis.