To approach the prevalence of age-related cataract and its relationships with the condition of examination, diagnostic criteria and geographical environment in various areas.According to the WHO's criteria of blindness and low vision, a statistical analysis of a national sample survey of blindness and low vision was carried out over the country.The number of patients with age-related cataract and visual acuity < 0.3 in both eyes calculated in the whole population was more than 5 million, the prevalence being 0.46%. The prevalence of blindness and that of low vision were 0.43% and 0.58% respectively. Among the blind, 41.06% was caused by cataract, and the low vision caused by cataract was 49.38%. Among elderly of >or= 60 years, the proportion of the blind and low vision caused by cataract was 73.13%. When the cataract standard was defined as lens opacity with visual acuity < 0.7, the prevalence of cataract was 5.99% in Beijing sample survey at the suburb area. The incidence of age-related cataract in females was significantly higher than that in males. In a survey of Beijing suburb in 1997, the prevalence of cataract among 5,084 elderly people of >or= 50 years with bilateral corrected visual acuity < 0.1 was 2.22%. In the southern part of China, the area of low latitude, especially in the plateau, such as in Guangdong Province (0.69%) and in Tibet (1.04%), the prevalence of cataract is much higher than that in northern part, high latitude areas, such as Heilongjiang Province (0.26%). A comparative study of the cataract prevalence of elderly >or= 40 years in the areas of different levels above the sea and sunshine times, it shows that the higher level above the sea and longer sunshine time the higher cataract prevalence.A longer sunshine time and a larger amount of ultraviolet irradiation are considered as the risk factors of cataract. Age-related cataract is the leading cause of blindness and the low vision in China.