There is no specific auxiliary examination index for oral ulcers, and the diagnosis cannot be made by the results of routine blood tests, but it needs to be diagnosed by the characteristics of medical history and clinical features, as follows. 1. History characteristics: oral ulcers are characterized by recurrent attacks, periodic attacks, and self-limiting nature that does not heal by itself. The length of the attack cycle varies, and it can be divided into the attack period, the healing period, and the intermittent period. 2. Clinical features: the ulcers are round or oval in shape, covered with yellow pseudomembrane, surrounded by a red halo band, central depression and obvious pain. Deeper and more serious ulcers may leave a scar after healing. If the above symptoms occur, it is recommended to go to the hospital in time to receive professional treatment as soon as possible.