Abstract：The theory of "external rheum treating the spleen and internal rheum treating the kidney" was established by YE Tianshi in the Qing Dynasty based on ZHANG Zhongjing's discussion on the treatment of rheum disease，which has a good guiding significance in clinical practice. The paper discusses the theoretical origin，connotation，principles and prescriptions of clinical application of "external rheum treating the spleen and internal rheum treating the kidney"， and lists three proved cases of the application of this theory to treat diseases.