Homologous recombination (HR) is an important biological activity in the cells, indispensable for the maintenance of genome integrity and stability and closely relative to the human health. In recent years, there is a great progress in this field. Here, we recapitulated four models of HR repair for DNA double-strand break, the mechanism for recombinase RacA/Rad51 action, and the regulation of Rad51 by Rad51 mediators involved in the process of Rad51 nuclear localization, Rad51 binding to ssDNA, homologous DNA pairing, strand invasion and exchange. It is helpful to profoundly understand the HR.