Persistent mouth ulcers, scientifically known as recurrent mouth ulcers, are a difficult disease to treat. According to Chinese medicine, mouth sores need to be treated with evidence, and the root cause is always “fire”. The actual fire should be cleared, but attention must be paid to the transformation of the type of evidence, never to the end, a single clear heat detoxification, especially the long-term use of a large number of bitter-cold drugs, that is, cold drugs, will lead to damage to the body’s Yang Qi, causing Yang Qi deficiency, which will cause the body’s immune system to decline, and even more diseases. The Chinese herbal ingredients of watermelon cream spray are: watermelon cream, forged borax, cypress, yellow dock, samphire root, eucalyptus, zhebei, Qing Dai, ice chips, rhubarb, Mu Han Guo (charcoal) baicalin, licorice, menthol. The main function is to clear heat and detoxify the toxin, reduce swelling and relieve pain. It is used for sore throat, sore mouth and tongue, swollen and painful gums or bleeding, acute and chronic pharyngitis, tonsillitis, stomatitis, mouth ulcers, pediatric thrush and bleeding from mild burns and wounds. In layman’s terms, it is used for real fire type mouth ulcers. This patient who has used a lot of watermelon cream spray and still has little success and has a history of up to 20 years is mostly suffering from deficiency fire mouth sores. In the case of deficiency fire mouth sores, one should distinguish between the internal organs, or focus on clearing first and then tonic, or focus on both attack and tonic.