The characteristic of Xiang(image)-Shu(number)thinking was reflected in Yun-Qi theory (doctrine of the five circuit phases and six atmospheric influences)in Huangdi’s Canon ofMedicine in the following aspects:the pattern of Yun-Qi,understanding of climate and phenophase,understanding of incidence of diseases,and understanding and application of medicines.In this theory,property of Xiang was systematically assigned to Shu,and Xiang and Shu were organized in a unique and complicated way to establish Yun-Qi pattern,by which climate,phenophase and incidence of diseases at a specific time were calculated,on the other hand,the status of Yun-Qi pattern was back-calculated based on metaphori-cal meaning of climate and phenophase.Xiang-Shu thinking also ran through the understanding and ap-plication of medicines of Yun-Qi theory,consequently different with later Chinese materia medica.So, the way of Xiang-Shu thinking would be helpful to master and apply Yun-Qi theory.