Abstract: miRNA, with full name of microRNA, is a kind of conservative non-coding single-chain RNA molecular, and its length was about 22 nucleotides（nt）. miRNA come from pre-miRNA of about 70 nt through Dicer enzyme cutting. miRNA is small, but it could combine with target mRNA and then form into complete or incomplete complementary condition to lead silencing complex to degrade mRNA or forbid its translation so as to play gene regulatory effect. miRNA plays an important role in animal growth,hormones secretion, cellular differentiation, cell proliferation and death, and carcinogenesis. The function of miRNA and correlation researches between miRNA and occurrence, development and transfering of tumour were reviewed.