Objective　Using Digital Simulation Technique(DST) to find and measure the optimum sacroiliac screw channel(OSSC) of the second sacral vertebra.　Methods　This study included 8 adult patients without pelvic disease admitted to the hospital In April 2011 to July 2011, and imports their pelvic CT scan data into Mimics for 3D reconstruction, and uses DST to establish the sacral cavity die, and uses the perspective of the sacral cavity die to determine the OSSC, and uses Space Analytical Geometry's (SAG) to measure it's parameters.　Results　All of the 8 cases (16 sides) can use DST to determine the OSSC of S2. The parameter of the OSSC of S2: The max radius is (6.38±0.54)mm in male, and(4.9±0.74)mm in female; The depth is (68.93±3.49)mm in male, and(58.43±8.16)mm in female; The angle with sagittal plane is (73.48±8.57)° in male, and(79.93±5.29)° in female; The angle with axial plane is (14.07±6.22)° in male, and(6.95±4.81)° in female; The angle with coronal plane is (7.12±7.11)° in male, and(5.87±5.01)° in female. The way to determine the initial point and the end point of OSSC: Draw a rectangle whose sides are horizontal or vertical to just right encircle the pelvic on the out-let pelvic X-ray films. Establish a 2-D rectangular coordinates whose origin is the lower left vertices of the rectangle, and point (0, 1) is the upper left vertices of the rectangle, and the point (1,0) is the lower right vertices of the rectangle. The coordinate of the initial point of OSSC is (0.5±0.26, 0.52±0.04) in male, and (0.49±0.24, 0.47±0.10) in female. The coordinate of the end point of OSSC is (0.5±0.01, 0.59±0.07) in male, (0.5±0.02, 0.49±0.14) in female. Use the same way to draw the rectangle and define the rectangular coordinates on the in-let pelvic X-ray films. The coordinate of the initial point of OSSC is (0.5±0.26, 0.52±0.04) in male, and (0.49±0.24, 0.47±0.10) in female. The coordinate of the end point of OSSC is (0.5±0.01, 0.78±0.01) in male, (0.5±0.02, 0.81±0.03) in female. Comparing between men and women, some parameters (the max radius, the depth, the angle with axial plane) have statistically significant difference(P<0.05),and the other have no statistically significant difference (P>0.05).　Conclusions　The DST can accurately determine the OSSC of S2.