Gene targeting is a rising technology in molecular biology,which is defined as the introduction of exogeneous DNA to specific site in genome by homologous recombination,and consequently change the hereditary character of the cell. This technology provides a new and powerful means for research in developmental biology,molecular genetics,immunology and medicine. Progresses have been made in exploring gene structure and function,gene expression and regulation,transgene and gene therapy with the application of gene targeting. But there are some problems in gene targeting,especially for the low efficiency. This article just provided a review of the principle and program of gene targeting,and discussed the possible approaches to increase the efficiency of gene targeting.