MicroRNAs, a class of noncoding RNA of approximately 22 nucleotides, can regulate gene expression by binding to the region of 3' UTR of the target mRNAs. To date, it has been demonstrated for organism that miRNAs play an important role in growth, development,and occurrence of disease. This paper introduces the character and the active mechanism of miRNAs, and the newest progress in the research on the function of microRNA, the identification of microRNA gene and the prediction of target gene also are summarized here.