OBJECTIVE: To measure the distances between the torus tubarius and different points of the petrous segment of the internal carotid artery to provide references to safe performance of cranial base surgery via transnasal endoscopic approach. METHODS: The study was carried out in 50 normal adults. The external aperture of internal carotid canal, foramen ovale, foramen lacerum were chosen as the landmarks of operation. The distances between these three foramen and the torus tubarius were measured separatively through threedimensional reconstruction in high resolution computer tomography. RESULTS: The measured distances between torus tubarius and foramen lacerum and external aperture of internal carotid canal were (17.440±0.213) mm and27.322±0.271) mm respectively. The distance between torus tubarius and foramen ovale of the right side was (22.000±0.323) mm, while those of the left side were (21.122±0.314) mm and (21.228±0.617) mm in male and female respectively. CONCLUSIONS: The study provides important references to avoiding the internal carotid artery injury,which is a fatal complication in cranial base surgery via transnasal endoscopic approach