A 39-year-old male patient had adenoid cystic carcinoma arising from the minor salivary gland at the right side of the soft palate. The tumor caused a local bony destruction of the pterygoid plate, invaded the pterygopalatine fossa and infratemporal fossa, and then spread upward into the middle cranial fossa via the foramen ovale and foramen rotundum. The primary tumor was silent and located at submucosa. The patient instead presented symptoms of intracranial tumor, such as severe headache and impairment of the 2nd and 3rd divisions of the trigeminal nerve. The anatomy of the skull base and the spreading routes of the oral tumor are discussed.