The severity of colonic ulcers with white moss needs to be combined with the ulcer size, morphology and pathological findings, which are usually not serious, but require timely and standardized treatment. Colon ulcers are limited defects or ulceration of the surface tissue of the colon mucosa observed under colonoscopy. The surface is covered with white moss, which is necrotic intestinal mucosa, and scarring usually remains after the ulcer heals. When a colonic ulcer is detected, it is necessary to observe its size, shape, depth and, if necessary, biopsy it to determine the nature of the lesion. Ulcers within 1 cm in diameter are small ulcers, 1 to 2 cm are large ulcers; more than 2 cm is a huge ulcer, most likely malignant ulcers. Morphological aspects of the observation of the ulcer around the inflammation of redness and edema, whether the central depression with white moss or yellow moss, microscopic observation of the ulcer with dirty moss, it is likely to be malignant lesions. Biopsy histopathology is very important, usually the ulcer is huge or bad shape, will take a biopsy, the pathological results are the most accurate. The presence of colonic ulcers covered with white moss, need to actively seek medical advice, follow the doctor’s instructions for rational treatment.