Abstract: The plant root system plays an important role in ecosystem matter exchange and energy flux, and root decomposition is one of the main contributors to these processes. Matter accumulates in roots and is then released back into the roots’ surroundings, including the atmosphere and soil, via the decomposition process. Root decomposition is affected by multiple biotic and abiotic factors. In terms of biotic factors, the chemical characteristics of roots are among the main factors affecting their decomposition. Other factors such as root lifespan, size/diameter, and the abundance and types of fungi and other microbes in soil also affect plant root decomposition, and their effects can be explained by their ability to alter the chemical characteristics of plant roots. Root exudates and changes in the abundance and activities of soil microorganisms that degrade plant roots affect the root decomposition rate. In terms of abiotic factors, water and temperature are the main factors affecting root decomposition. Other factors related to climate change, for example, nitrogen deposition and carbon dioxide concentrations, will affect the root decomposition rate to different degrees, the extent of which is currently unknown. In this study, we reviewed the process of matter release during plant root decomposition, and summarized the current knowledge on how different biotic and abiotic factors affect plant root decomposition. Finally, we proposed some related perspectives based on the current status of plant root decomposition research.