Postinfectious cough is very common in clinical practice, which is not sensitive to current medical treatment. On traditional Chinese medicine theory, postinfectious cough belongs to "nondiffusion of lung", and we expect that the traditional Chinese herbal medicine and decoction are effective to postinfectious cough. This case is a thirteen-year-old boy suffered from persistent cough lasting one week after getting cold. After accepting treatment of Decoction of Ramulus Cinnamomi plus Magnoliae Cortex and Apricot Fruit (Gui Zhi Jia Hou Po Xing Zi Tang), his cough symptom has been completely relieved. This case indicated that Decoction of Ramulus Cinnamomi plus Magnoliae Cortex and Apricot Fruit can treat postinfectious cough effectively. This article aims to explore the cause of postinfectious cough, the etiology and pathogenesis of TCM about this boy, and the mechanism of the Decoction of Ramulus Cinnamomi plus Magnoliae Cortex and Apricot Fruit on the basis of Sheng Nong's Herbal Classic.