Abstract: With the continuous progress of science and technology, haze phenomenon occurs frequently, PM_2.5 was the main component of haze. Long-term or short-term exposure to high concentrations of PM_2.5 may have a certain impact on human health, which was not only a hot social issue on industrial production and environmental health, but also a focus of research among domestic and foreign scientists. Numerous studies have shown that PM_2.5 can cause respiratory, cardiovascular, immune and reproductive systems, and even can cause inflammation; severe exposure can lead to death. This article reviewed the chemical composition and sources of PM_2.5, research methods and its effect on human health.