With the deterioration of global environment and the westernization of our national diet, the incidence of colorectal cancer in China is gradually increasing due to the high-fat and high-calorie diet, but colorectal cancer itself is a preventable disease. Although the symptoms of early colorectal cancer are not specific, they can be seen from the details. How to stop the derivation of colorectal cancer at the source, we can start from observing the stool. 1.Change of stool frequency: increase or decrease The normal stool frequency is about 3 times/day-3 days/time, once the habit of stool frequency changes, increases or decreases, it is necessary to be alert. 2. Change of stool characteristics: diarrhea or constipation, thinning The stool of the left hemicolectomy (left area of transverse colon, descending colon, sigmoid colon) has been formed. If the tumor grows in this intestinal segment, it is accompanied by constipation or diarrhea alternately, and the stool is often accompanied by mucus or blood; when the tumor grows gradually, it even appears obstruction. In early stage, most of the symptoms of rectal cancer are blood in stool, similar to hemorrhoids; in late stage, due to narrowing of intestine, stool will become thinner, flatter and even obstructed. 3. Change of stool color: blood in stool Most of the symptoms of blood in stool are persistent, chronic blood with mucus, mixed with feces. The right hemicolectomy lumen is wider, the intestinal wall is thin, and the contents of the intestinal cavity are mostly in semi-fluid form, so blood is mixed with semi-fluid stool and stays in the intestinal tract for a longer time, thus showing dark red blood stool. 80% of rectal cancers are associated with blood in stool, mostly bright red blood stool. Not all colorectal cancer lesions have blood in the stool, and intestinal bleeding may not always be caused by cancer. Therefore, regardless of the occurrence of blood in the stool and changes in stool habits, it is necessary to consult a doctor promptly for early and symptomatic treatment.