Background <p>Cesarean scar pregnancy (CSP) is defined as a gestational sac or trophoblast implanted within the previous cesarean scar (CS). This study aimed to investigate the mechanism of CSP.</p> Methods <p>We collected the decidual tissues from the cesarean scar (<i>n</i> = 25) and the uterine cavity (<i>n</i> = 25) of the same women at the department of Gynecology, Maternal and Child Health Hospital of Hubei Province, Tongji Medical College, Huazhong University of Science and Technology from July to December 2023. We examined the morphological changes and angiogenesis in the decidual tissues and investigated the expression of factors related to endometrial recovery. Scanning electron microscope was used to detect the number of pinopodes.</p> Results <p>Compared to the CSP-cesarean cavity group, the CSP-uterine scar group exhibited more diffuse lymphocyte infiltration in the decidual tissues. The vessel density (31.95 vessels/mm²) was significantly lower in the CSP-uterine scar group than in the CSP-cesarean cavity group (69.4 vessels/mm², <i>P</i>&lt;0.0001). The vascular surface (0.0180 ± 0.0018 mm²/mm²) and luminal surface area (1,871.00 ± 352.65 m²/vessel) were significantly smaller in the CSP-uterine scar group compared with the CSP-cesarean cavity group (0.0550 ± 0.0031 mm²/mm² and 2,930.00 ± 548.14 µm²/vessel, <i>P</i>&lt;0.0001). Compared to CSP-cesarean cavity group (7.00 ± 1.00), the number of pinopodes were significantly decreased in the CSP-uterine scar group (0.33 ± 0.58). The expression levels of CD56, IL-6 and IL-1β were significantly lower in CSP-uterine scar group than that in the CSP-cesarean cavity group.</p> Conclusions <p>Cesarean scar decidual tissues exhibit reduced angiogenesis and endometrial receptivity. The altered vascular patterns in cesarean scar decidual tissues may facilitate embryo implantation.</p>