Studies have shown that there are lots of species and quantities of pathogenic bacteria and viruses in air, water, soil and other environments, and these pathogenic microorganisms are closely related to the spread and epidemic of some important infectious diseases. Therefore, it is really important to detect the dynamic conditions of pathogenic bacteria (species, quantity, change trend, etc.) in the environment regularly. In the past, isolation and culture were used for detection, which is not only time-consuming, but also unable to detect some pathogens that are difficult to be cultured manually. PCR technology can overcome the above defects and normally only take 2-4 hours to get results.With the continuous development and improvement of PCR technology, PCR technology has been widely used in environmental microbiology. At the beginning of the establishment of PCR technology, environmental microbiology workers in various countries began to use this technology to detect specific microbial groups or genotypes in the environment. In recent years, with the continuous improvement of specificity and sensitivity of PCR technology, the research of environmental microbiology workers is mainly focused on the following two aspects: 1. Using PCR technology to study the composition and structure of the microbiota in a particular environment, and then to understand the population dynamics. 2. The application of PCR technology to monitor the dynamics of specific populations (such as pathogenic bacteria and engineered strains) in the environment.