[Objective]To summarize the characteristics and experience of Professor ZHANG Deying in treating acne from the perspective of phlegm syndrome.[Methods]By following the clinical study of Professor ZHANG's clinic,the medical records of acne treatment were sorted out,three typical cases were selected,and combined with the classical theories of traditional Chinese medicine,the unique insights and clinical experience of Professor ZHANG on phlegm syndrome theory were analyzed and summarized.[Results]According to the physical condition of people and the characteristics of acne,Professor ZHANG points out that the etiology and pathogenesis of acne are phlegm heat or phlegm fire invading the head,chest and causing local flesh rot.According to the spleen and stomach of middle-Jiao,the phlegm is a pathogenic factor of soil.In the treatment,the purpose of reducing phlegm can be achieved by reducing soil,multiplying wood to reduce soil and producing metal to eliminate soil,and then using heat-clearing drugs to clear the evil of upper-Jiao phlegm heat and cure acne.At the same time,it should be noted the relationship among the five elements,the phlegm is too excessive,easy to block the kidney water and cause kidney deficiency,the first treatment is reducing phlegm,after the removal of phlegm,tonifying the kidney can be effective,even some patients do not need to be tonified the kidney,and the kidney will slowly recover.[Conclusion]Professor ZHANG has unique understanding of the theory of phlegm syndrome,pointing out that the pathogenesis of acne is mostly phlegm fire or phlegm heat stagnation in the muscle surface,and the flesh rot.The main treatment should be to clear phlegm heat.Phlegm is the pathogenic factor of soil.Besides the method of reducing soil,according to the theory of five elements,there are also methods of multiplying wood to reduce soil and producing metal to eliminate soil.