As a microbial flora distributed in the human intestine, the intestinal flora plays an important part in the normal physiological function of the intestine. Clinical studies have revealed that extensive use of broad-spectrum antimicrobials breaks the balance of the intestinal flora, leading to antibiotic-associated diarrhea (AAD). However, the relationship between different intestinal flora and AAD is not identical. This paper reviews the mechanism of AAD caused by pathogenic bacteria, the principle of prevention and treatment of AAD by probiotic, and the relationship between conditional pathogens and AAD in order to provide theoretical basis for the study of intestinal flora and AAD. At the same time, it provides references for more accurate prevention, diagnosis and treatment of AAD.