To investigate the anatomic feature of the posterior hip joint capsule and its distributional difference of collagen fibers and to probe the optimization of the capsulotomy which can reserve the best strength part. Methods Ten adult cadaver pelvises (6 males and 4 females, aged 28-64 years) fixed with formal in were used. Ten right hips were used for anatomical experiment of hip joint capsule. The posterior hip joint capsules were divided into 3 sectors(I-III sectors ) and 9 parts (IA-C, IID-F, IIIG-I). The average thickness of each part was measured and the ischiofemorale l igaments were observed. Five capsules selected from ten left hips were used for histological experiment. The content of collagen fibers in sector I and sector II was analyzed by Masson’s staining. Two fresh frozen specimens which were voluntary contributions were contrasted with the fixed specimens. The optimal incision l ine of the posterior capsule was designed and used. Results The thickness in the posterior hip joint capsule [IA (2.30 ± 0.40), IB (4.68 ± 0.81), IC (2.83 ± 0.69), IID (2.80 ± 0.79), IIE (4.22 ± 1.33), IIF (2.50 ± 0.54), IIIG (1.57 ± 0.40), IIIH (2.60 ± 0.63), IIII (1.31 ± 0.28) mm] had no uniformity (P lt; 0.01). The IIIG part and the IIII part were thinner than the IB part and the IIE part (P lt; 0.01). Two weaker parts located at obturator externus sector (sector III), the ischiofemorale l igament trunk went through two thicker parts (IB and IIE). The distribution of the collagen fibers in sector I and sector II(IA 20.34% ± 5.14%, IB 48.79% ± 12.67%, IC 19.87% ± 5.21%, IID 17.57% ± 3.56%, IIE 46.76% ± 11.47%, IIF 28.65% ± 15.79%) had no uniformity (P lt; 0.01). The content of collagen fibers in IB part and IIE part were more than that of other parts (P lt; 0.01). There were no statistically significant difference in the distribution feature of the thickness and the ischiofemorale l igaments between the fresh frozen specimens and the fixed specimens. The optimal incision l ine C-A-B-D-E of the posterior capsule was designed and put into cl inical appl ication. The remaining capsular flap comprise the most of the ischiofemorale l igament trunk and the part of gluteus minimus. Conclusion Although enhanced posterior soft tissue repairin total hip arthroplasty was investigated deeply and obtained great development, but the postoperative dislocation rate was not el iminated. It is significant for optimizing the capsulotomy to reserve the best strength part of the posterior capsule and to bring into full play the function of the ischiofemorale l igaments.