Acute kidney injury (AKI) presents as a sharp decline in renal function caused by a variety of reasons. It is a severe clinical challenge affecting multiple organs and multiple systems, with high mortality. Continuous renal replacement therapy (CRRT) plays an important role in the treatment of AKI. Limited by the lack of evidence, the timing of CRRT for AKI remains ambiguous. This article reviews the definition and grading of AKI, the indication and the timing of initiation/termination of CRRT for AKI .