With the rapid increase in the number of colonoscopy consultations, especially the expansion of the scope of microscopic treatment, safety issues have emerged. The following complications may occur during colonoscopy due to inappropriate selection of indications, inadequate preparation before the procedure, and lack of operator experience: 1) perforation of the intestinal wall; 2) intestinal bleeding; 3) mesenteric and plasma membrane tears and splenic rupture; 4) cardiac arrest and respiratory depression. Although the incidence of these complications is very low, when they do occur they can cause unnecessary illness, unnecessary financial cost, and even cost of life to the subject. The outcome of complications is closely related to whether they are detected in time and handled appropriately. Therefore, early detection is very important. If there is persistent abdominal pain or blood in the stool after colonoscopy be sure to notify your own doctor so that early action can be taken.