Abstract: In the environment, about 99% microorganisms have not been or can not be cultured by traditional cultivation approach. With the development of molecular biology and its application in microbiology, a new research field of metagenomics has emerged. Without prior isolation and cultivation of relative microorganisms from environmental samples, metagenome libraries are constructed by extracting DNA from environmental samples and transforming it to surrogate host. This review explains unculturability of microorganisms from the point of ecology. Metagenomics can be used for bioremediation of polluted soils and deodorization of animal manure. Furthermore, microorganisms are of immense significance in the collection, investigation and exploitation of genes in uncultured microorganisms.