Objective To explore the difference in ocular biologically effective ultraviolet irradiance in two areas with different altitudes ,Xichang and Shaoxing,and provide a reference basis for ocular UV protection. Methods A self?designed rotating mannequin and dual?detector spectrome?ter were used to monitor the intensity of ocular exposure to UV irradiation under clear skies in Xichang and Shaoxing. Monitoring data were pro?cessed and analyzed with AvaSoft 7.4 USB2 software and OriginPro 8.0 software. Results The diurnal variations of ocular biologically effective ul?traviolet irradiance exhibited bimodal distribution in Xichang and Shaoxing. The maximum UVBEcorn,UVBEconj,and UVBElens of Xichang were about 1.7 times,2 times,and 1.8 times that of Shaoxing,respectively. Under the same solar elevation angle,the biologically effective ultraviolet irra?diance of the cornea,conjunctiva,and lens in Xichang were higher than those of Shaoxing. Conclusion The diurnal variations of ocular biologi?cally effective ultraviolet irradiance exhibit bimodal distribution in areas at two different altitudes. Under the same solar elevation angle ,the biologi?cally effective ultraviolet irradiance of the cornea,conjunctiva,and lens of Xichang are significantly higher than those of Shaoxing.