Objective:To investigate the distribution of intraocular pressure (IOP) in high-altitude population aged 18 years and over in Xining, Qinghai and establish the reference interval (RI) of IOP.Methods:A cross-sectional study was conducted in Xining, Qinghai Province at 2.271 km above sea level from September 2019 to May 2020.Ophthalmic examinations and IOP measurement were conducted among subjects from Physical Examination Center of Qinghai Provincial People's Hospital.The subjects who had been living in Xining without leaving for three months were enrolled.Ophthalmic examinations included vision examination, IOP measurement, slit-lamp microscopy, fundus photography, anterior and posterior segment optical coherence tomography.IOP was measured using Goldmann applanation tonometry under local anesthesia.Subjects with factors that could cause significant changes in IOP and affect the accuracy of IOP measurement, and those who were unable to receive IOP measurement were excluded.Subjects were grouped according to sex, age and ethnicity, and the distribution and RI of IOP were compared among all groups.This study adhered to the Declaration of Helsinki.The study protocol was approved by the Ethics Committee of Beijing Tongren Hospital, Capital Medical University (No.TRECKY2017-024). Written informed consent was obtained from each subject.Results:A total of 6 120 subjects (6 120 eyes) aged 18-90 years old were enrolled, including 2 850 males and 3 270 females with average age of (45.54±13.85) years.The average IOP of high-altitude population in Xining, Qinghai Province was (14.32±1.93) mmHg (1 mmHg=0.133 kPa), with the RI of 10.54-18.10 mmHg.The average IOP was (14.42±1.98) mmHg in male with the RI of 10.54-18.30 mmHg, (14.23±1.88) mmHg in female with the RI of 10.55-17.91 mmHg.The IOP of male was higher than that of female ( t=3.71, P<0.001). The IOP of Han, Tibetan, Hui and other nationalities were (14.38±1.91), (13.93±2.06), (14.21±1.87), (13.94±1.95) mmHg, respectively, with a statistically significant overall difference ( F=6.73, P<0.001). The IOP of Han nationality was significantly higher than that of Tibetan, Hui and other nationalities, and the differences were statistically significant (all at P<0.05). Conclusions:RI of IOP in high-altitude population from Xining, Qinghai is lower compared with normal altitude area.