Mixed tumor of parotid gland, also known as pleomorphic adenoma, is the most common benign tumor in clinic, patients usually have no obvious symptoms, and it can occur at any age, and its growth rate is relatively slow, but the following situations suggest the possibility of malignancy: firstly, mixed tumor of parotid gland has a thin periosteum, so it is prone to recurrence in the event of improper surgery. However, its malignant rate is relatively low, about 5%. When the growth rate of the tumor suddenly increases, accompanied by nerve paralysis, pain and other symptoms, then beware of the risk of malignant transformation; second, benign mixed tumor of parotid gland exists for a long time, recurs more often, and the volume of the tumor is relatively large, and when the diameter exceeds 5cm or has received radiotherapy, etc., all of them can make the chance of malignant transformation increase; third, if the mixed tumor of parotid gland is shown in the pathology and there are Thirdly, if the mixed tumor of parotid gland is shown pathologically, there are lesions such as small focal hemorrhagic necrosis, extensive vitreous degeneration, ossification and calcification, etc., or the peripheral membrane of the tumor is incomplete. In all these cases, the possibility of malignant transformation should be highly alerted.