Abstract: We developed a protocol for three-dimensional (3D) annotation and segmentation of the facial nerve canal and measured the length parameters of each segment in healthy individuals to provide preliminary quantitative reference data. Ultra-high-resolution computed tomography (U-HRCT) images of the temporal bone were acquired from 47 healthy individuals. A 3D manual annotation protocol for the entire course of the facial nerve canal was established, and 3D reconstruction was performed. A four-segment classification scheme for the facial nerve canal was proposed by identifying the following anatomical landmarks: the labyrinthine, geniculate ganglion, tympanic, and mastoid segments; the length of each segment was measured as 2.89 (2.31, 3.64) mm, (2.52 ± 0.86) mm, (11.75 ± 2.16) mm, and (16.06 ± 2.07) mm, respectively. The total length of the facial nerve canal was (33.31 ± 1.97) mm. Statistically significant differences were observed among the lengths of the four segments, with the mastoid segment being the longest, followed by the tympanic. The labyrinthine and geniculate ganglion segments were the shortest, with no statistically significant differences between them. By establishing a facial nerve canal annotation protocol and proposing a four-segment classification that includes the geniculate ganglion as an independent segment, this study provides preliminary quantitative reference data for normal adult facial nerve canal lengths. These findings provide a reference for imaging studies on facial nerve-related diseases and establish a foundation for the future development of automated measurement algorithms.