Objective　To investigate the safe position of the plates and safe angles of the screws through measurement of the parameter of the acetabulum and virtual plate-screw placement in the three-dimensional posterior wall of the acetabulum.　Methods　The thin slice CT data of 50 pelvics and 15 normal cadavers were used in this study. Three-dimensional reconstruction of pelvics were achieved by Mimics 10.0; then the virtual 3-dimensional acetabulum was resliced ,and the transverse, longitudinal diameter of the acetabulum and the width of the posterior wall of the acetabulum were measured, respectively. The virtual plate was designed by the software of Solidworks2010 and was introduced into the software of Mimics 10.0. The position of the plates and the angle of the screws were measured and the safe zones of the plate and the safe angles of the screws were deduced. Based on the above-mentioned data, the plates were fixed on the 30 posterior walls of the acetabulum 6mm away from the posterior edge of the acetabulum.   Results  The longitudinal and transverse diameter of the acetabulum were 55 mm and 52 mm, respectively. The widest width of posterior wall was 51 mm, which was at the superior edge; The narrowest was 38 mm，which was at the edge of middle-lower part of the posterior wall. When the screws could be drived into the hole of the plates, the smallest angle between the reconstructive plate and the screws were from 50° to 66°. The screws were not inserted into the acetabulum ,when plate-screw fixation were palced in the posterior wall of the acetabulum in cadavers 6mm away from the lateral edge of acetabulum.   Conclusions   When the plate is at least 6mm away from the posterior edge of the acetabulum, the screws could safely avoid entering the hip joint. As the distance of the plate away from the lateral edge of the acetabulum grows, the safe range of for screw placement increases.