Background: Mounting evidence shows that vascular factors play an important role in the pathogenesis of glaucoma, while optical coherence tomography angiography (OCTA) can provide a better view for microvascular changes in glaucoma. Objective: This study aimed to assess the effect of the severity of acute primary angle closure glaucoma (APACG) on macular microcirculation and the diagnostic value of blood flow and macular structure for APACG using OCTA. Methods: Patients with APACG hospitalized at the Tianjin Eye Hospital from January to April 2019 were enrolled in this prospective cohort study. They were assigned to mean deviation (MD) ≤6 (35 eyes), 6 < MD ≤ 12 (41 eyes), MD >12 (33 eyes), primary angle closure suspect (PACS) (40 eyes), and age-matched agerelated cataract (ARC) groups (33 eyes). OCTA was used to measure the vessel density (VD) and foveal avascular zone (FAZ) in different macular superficial areas. OCT was used to measure the retinal thickness (RT) and ganglion cell complex thickness (GCC). One-way analysis of variance was used to compare the differences in VD and FAZ for different degrees of APACG. Areas under the receiver operating characteristic curves (AUCs) were used to assess the diagnostic values of VD, RT, and GCC for APACG. Results: On comparing the ARC, PACS, and MD ≤6 groups with 6 < MD ≤ 12 and MD > 12 groups, differences in all parameters were found to be statistically significant. This indicated that VD gradually decreased and FAZ enlarged with the exacerbation of APACG. For the 6 < MD ≤ 12 group versus PACS group, the diagnostic value of VD was high (AUCs: 0.902-0.942), and that of RT was moderate (AUCs: 0.805-0.842). For the MD >12 group versus PACS group, the diagnostic values of VD (AUCs: 0.900-0.958) and RT (AUCs: 0.828-0.887) increased. Conclusions: With the exacerbation of APACG, the damage of VD in the macula was greater. VD had higher diagnostic accuracy, providing a new view for the diagnosis of APACG.