Acute kidney injury (AKI) has been recognized as a major healthcare problem affecting millions of patients worldwide, and is associated with a substantial increase in morbidity and mortality. AKI occurs in about 13.3 million people per year, 85% of whom live in the developing world, is thought to contribute to about 1.7 million deaths every year. A meta-analysis showed that the incidence of AKI was 21.6% in adult hospitalized patients worldwide and the incidence was 0.99%-11.6% in China. The incidence and mortality of AKI patients in intensive care unit are higher than general ward, with a poor long-term prognosis. The epidemiological results of AKI varies widely among studies. Overall, epidemiological results of AKI in high income countries of multicenter, large sample studies are from large databases, but lack of prospective studies. There are few high quality studies of AKI in the low and middle income countries. In recent years, great progress has been made in epidemiological studies in china.