Exogenous febrile disease， with fever as its main symptom， is caused by the evil Qi which invades the human body. Children’s viscera and their bodies are immature and delicate， so their Yang is susceptible to exogenous pathogenic factors. If the treatment principle is limited to clearing the heat and relieving the toxicity， the situation may be worse. Mr. Xu Xiaopu， a famous pediatrician of Chinese Medicine in Shanghai， master Huangdi Neijing and Nan Jing. He epitomized the thoughts of cool and warm. By using the principles of warming the spleen Qi and the kidney Qi， strengthening Yang and the using Herba Ephedrae and cassia twig， Mr. Xu always got marked effects. "The Xu Pediatrics"， developed from Mr. Xu Xiapfu， emphasizes on the principle of reliving exterior with warmth and acridity， strengthening the body resistance to eliminate pathogenic factors and so on. Learning from "The Xu Pediatrics"， the writer not only explores the pathogenesis and treatment of exogenous febrile diseases， but also the importance of "strengthening Yang" theory.