The irritable bowel syndrome (IBS) is a kind of disease syndrome composed of such characteristics as abdominal pain, abdominal distension, bowel habit and abnormal defecate character, symptom persistence or intermittent attacks, abnormal biochemical indicators without morphology. It is a disease of bowel function disorder with higher morbidity, whose clinical manifestation is complex and varied. And it is divided into three clinical syndromes of diarrheic type, constipation type and alternating diarrhea and constipation type. The changing condition of intestinal flora has been analyzed for IBS patients through research and observation. This paper has studied the dissociation effect of applying probiotics in curing irritable bowel syndrome of IBS patients and its function of balancing microflora. This paper has found that: 1. there exists abnormal intestinal flora among IBS patients, and it represents the phenomenon of decreasing anaerobic probiotics such as bifid bacterium and lactobacillus etc, the increase of aerobic bacteria such as enteric bacilli, as well as the weakening colonization resistance of intestinal tracts, which suggests that there exists alteration of intestinal flora among IBS patients, and dysbacteriosis maybe one of the important causes of IBS.