Abstract: Microplastics are plastic fibers, particles, or films with a particle size of less than 5 mm. They are widely found in water, soil, and atmospheric environments. Because of their small particle size, large surface area, strong adsorptive capacity and other characteristics, they can adsorb heavy metals, persistent organic pollutants, environmental endocrine disruptors and other substances. When humans are exposed to microplastics, the particles can not only have toxic effects on the contact sites, but also penetrate tissue barriers and acess other organs, potentially causing systemic toxic effects. Existing epidemiological and toxicological studies have shown that microplastics can cause damage to the digestive, respiratory, nervous and reproductive systems. However, their bio-distribution, metabolic characteristics and toxic mechanisms have not been fully clarified. This study provides a systematic review of the absorption, distribution, metabolism and excretion characteristics of microplastics in living organisms. By integrating factors such as particle size and chemical composition, this study also investigates the toxic effects of microplastics on multiple organ systems (e.g., digestive and nervous systems) and key organs (e.g., intestine and liver), as well as the underlying molecular mechanisms. The aim is to provide a scientific basis for a comprehensive assessment of the health risks of microplastics and to offer theoretical support for the development of relevant prevention and control strategies.