microRNA(miRNA) is a type of endogenous small non-coding RNA in eukaryotes with a length of about 17~25nt. Since the discovery of miRNAs in 1993, the advances and discoveries of small RNA have upended the scientific understanding of gene regulation. From embryonic development to apoptosis, and tumor growth, miRNAs play an important role in a range of physiological and pathological processes, and various miRNAs related to genetics, metabolism, infectious diseases or tumors have presented a new perspective for scientists to conduct pathological research, and it may become a reliable biomarker for disease. Scientists are also actively changing the function of miRNA and developing new in vivo delivery methods to seek interventions. Recently, miRNAs have been used to mediate the cross-specie evolution and adaptation.