Objective: To investigate the anatomical features of the safe zone for sacral lateral mass screw placement and find the safe trajectory, so as to provide reference for clinical application. Methods: The three-dimensional computed tomography scan materials of sacrococcygeal vertebrae in 60 patients admitted to the Liaocheng People's Hospital of Shandong Province were analyzed by Mimics software to establish three-dimensional models. There were 33 males and 27 females, aged 25-78 years, with an average age of 45.7 years. After the safe zone was separated from sacral lateral mass model, a maximum cylinder was placed into the safe zone according to its anatomical feature. The cylinder was established as safe trajectory. Anatomical data were measured, including the length and diameter of screw trajectory, the distance between the entry point and the middle jaw, and adjacent upper and lower foramen, as well as the intersection angle between the screw direction and sagittal plane, between the screw direction and the adjacent upper end plate. Results: The restriction factor of screw size on S₁, S₂ lateral mass was transverse diameter, while the restriction factor on S₃, S₄ was the distance between adjacent intervertebral foramen. The maximal length of screw from S₁ to S₄ was 30 mm, 35 mm, 30 mm, 14 mm respectively, while the maximal diameter was 12 mm, 9 mm, 5 mm, 5 mm respectively. The best entry point of S₁ mass screw was lateral to the zygopophysis. The best entry point of S₂-S₄ mass screw was located at the midpoint of a line connecting the lateral edge of adjacent posterior sacral foramen approximately about 2 cm from median sacral crest. The leaning angles of screw was increased successively, and the sagittal plane was slightly inclined. There were significant differences between male and female groups in the leaning angle in S₂ [male: (35.8±1.2)°, female: (37.9±3.7)°] and the distance between entry point and median sacral crest [male: (20.5±1.0)mm, female: (19.1±1.4)mm](P<0.05), while there was no significant difference in other parameters (P>0.05). Conclusions Cylindrical bony channel which is feasible for screw placement can be found in the lateral mass of sacrum. Individualized measurement can provide reference for application of lateral mass screw.