Inflammatory bowel disease (IBD) is an incurable disease of the digestive system; however, the therapeutic methods for IBD remain limited. The pathogenesis of IBD was systematically discussed and compared in this paper, primarily comprising Crohn's disease and ulcerative colitis. This paper focused on six common aspects: (1) Dysregulated immune responses; (2) Gene function changes; (3) Intestinal microbes disorder and imbalance; (4) Microbial infections; (5) Associations between IBD and other inflammatory diseases; and (6) Other factors. In addition, the pathogenesis differences between these two forms of IBD were unraveled and clearly distinguished. These unique aspects of pathogenesis provide crucial insights for the precise treatment of both Crohn's disease and ulcerative colitis. This paper illustrates the root causes and beneficial factors of resistance to IBD, which provides novel insights on early prevention, development of new therapeutic agents, and treatment options of this disease.