Objective:To investigate the optic nerve subarachnoid space area (ONSSA) in patients with normal tension glaucoma (NTG) and primary open-angle glaucoma (POAG) and its correlation with related factors.Methods:Fifty-three patients with NTG (Group A) and 46 patients with POAG (Group B) were selected from January 2016 to May 2019 in Gaozhou Traditional Chinese Medicine Hospital of Guangdong Province. None of them received any treatment. Another 40 patients with health examination (Group C) were selected. Body mass index, blood pressure, 24-hour intraocular pressure, visual field damage, visual axis length and central corneal thickness were measured in each group. Two-dimensional ultrasound was performed to analyze the difference of ONSSA in the retrobulbar 3 to 7 mm range in each group, and the correlation between ONSSA and clinical related factors was analyzed.Results:The ONSSA in group A was significantly smaller than that in group B and group C: (5.07 ± 0.83) mm 2 vs. (6.19 ± 0.90) and (6.57 ± 1.43) mm 2, the differences were statistically significant ( t = 5.219 and 6.107, P < 0.05). ONSSA in group A was positively correlated with the mean intraocular pressure and maximum intraocular pressure of 24 hours ( r = 0.658 and 0.479, P < 0.05), while ONSSA in group B and C was not correlated with the mean intraocular pressure and maximum intraocular pressure of 24 hours ( P > 0.05). ONSSA was not correlated with age, body mass index, mean arterial pressure, central corneal thickness, visual field damage and visual axis length ( P > 0.05). Conclusions:ONSSA of NTG patients is lower than that of POAG patients and healthy people, and the ONSSA of NTG patients is correlated with the mean intraocular pressure and maximum intraocular of 24 hours.