Objective: To compare the ocular biometric parameters between the acute primary angle closure (APAC) eyes and the fellow eyes as well as the risk factors associated with APAC. Methods: From January 2008 to March 2020,222 monocular APAC patients over 45 years old from the Glaucoma Department of Zhongshan Ophthalmic Center, Sun Yat-sen University were retrospectively studied. Patients with binocular attack, previous attack in the fellow eyes, and secondary factors such as lens-induced and traumatic glaucoma were excluded. Ocular biometric parameters including axial length (AL) and lens thickness (LT) were measured with A-scan ultrasound, while the anterior chamber depth (ACD) was measured by ultrasonic biological microscope. AL, ACD, LT and relative lens position (RLP) were compared between the APAC and the fellows eyes. Results: The average age of onset was (62.57±9.14) years. The ACD was (1.75±0.27) and (1.88±0.31) mm, AL was (22.34±0.80) and (22.35±0.83) mm,LT was (5.14±0.38) and (5.17±0.42) mm, and the RLP was 0.195 and 0.198 for the APAC and the fellow eyes,respectively. Compared with the fellow eyes, the ACD of the APAC eyes was shallower, and the RLP was more anterior (both P<0.001), while the differences of AL and LT were not statistically significant (both P>0.05).Furthermore, AL of patients with a younger age of onset (aged 45 to 59 years) was shorter than that of those with an older age of onset (aged 60 to 69 or over 70 years); patients with an onset age of over 70 years have shallower ACD and more anterior RLP, all statistically significant (P<0.05). In addition, correlation analysis indicated that younger onset age was significantly correlated to shorter axial length of APAC eyes (P<0.001). Conclusion:APAC eyes had shallower ACD and more anterior RLP. Shorter AL and female were associated with APAC attack between individuals. Shallower ACD, thicker lens and more anterior RLP are potential risk factors for APAC among aged population.