In recent years, research on cancer has begun to turn to human genomic miRNAs. MicroRNAs (miRNAs), called microRNAs, are a class of endogenous non-coding RNAs with regulatory functions found in eukaryotes, which have small variation and play a stable and persistent role in gene transcriptional regulation. Only a small fraction of miRNAs have been elucidated for their biological functions. These miRNAs regulate cell growth, tissue differentiation, and are therefore associated with development and disease in life processes. Laboratory analysis of miRNA loci on the genome can show that they are associated with the development of many cancers and play a crucial role in tumor development. miRNAs play a role similar to the function of oncogenes and oncogenes. let-7 was the first oncogene identified, and let-7 expression was significantly reduced in cancerous tissues in lung cancer patients compared with normal lung tissues. Experiments have also demonstrated that the lower the level of let-7 expression in non-small cell lung cancer patients, the worse their prognosis. On the contrary, if the level of let-7 expression in human body is increased, the proliferation of tumor cells can be inhibited. The functions of some other miRNAs are also being gradually elucidated, for example, mir-143 and mir-145 are significantly down-regulated in colon cancer, and the 11q924 locus is often missing in patients with breast, lung, ovarian and uterine cancers, etc. It is reasonable to believe that miRNAs family will play an important role in the diagnosis, treatment and prevention of tumors, and write a new chapter in the history of human anti-cancer medicine.