Objective    To explore the surgical safe zone of the anterior plate and screw fixation for treating sacroiliac joint fracture and dislocation.   Methods    15 normal pelvic specimens were used. The horizontal distances from L4, L5 anterior roots to the sacroiliac joint, the vertical distances from L4, L5 roots to sacral wing, the distances from the intervertebral foreman of L4, L5 to the rim of true pelvis, and the diameter of the L4, L5 roots were measured respectively. On two dimensional pelvic coronal reconstruction images, the angle between sacroiliac joint and sagittal plane, the width of the sacrum were tested.    Results    The horizontal distance from the lateral side of the L4, L5 roots to the sacroiliac joint gradually diminished from the top to the bottom, with the widest of (2.1±0.2）and （2.7±0.2）cm  respectively, and the narrowest of （1.2±0.2）cm and（1.5±0.2）cm respectively. The vertical distances between the L4 root and the sacrum also diminished gradually from the intervertebral foramen to the rim of the pelvis. The length of the L4 and L5 roots were（7.4±0.8）cm and 3.9±0.5）cm, and the diameters  (2.7±0.8）mm and （7.3±1.4）mm respectively. On CT reconstruction images, the angle between sacroiliac joint and sagittal plane was about 30°, and the distance from the sacroiliac joint to the lateral side of the spinal canal changed from 3.3cm to 2.3cm, the horizontal distance from the sacroiliac joint to the lateral side of the intervertebral foramen was about 2cm.    Conclusions    The surgical safe zone of the anterior plate and screw fixation for treating sacroiliac joint fracture and/or dislocation can be defined as the follows: the upper and lower plates places on the upper third of the sacroiliac joint, with the limited exposure range of 2.5cm, or the middle third of the sacroiliac joint, with the limited exposure range of 1.5cm. The screw should be inserted with introversional angle of 300.