Natural starch is one of the end products synthesized by green plants through photosynthesis, and is one of the main storage polysaccharides in the harvesting organs of crops and one of the key raw materials supporting the development of modern industry. The molecular weight of starch is an important fundamental parameter for studying the molecular structure of starch and is also an important basis for determining the properties and applications of starch. By modulating the molecular weight of starch, many properties of natural starch can be improved, such as thermal stability, gel strength, rheological properties, making the starch more suitable for applications in the pharmaceutical, chemical and food industries, which has become a hot research topic in recent years. This paper reviews summarizes and analyzes the research on the regulation of starch molecular weight from three aspects: physics, chemistry, and biotechnology, and discusses the mechanisms of different regulation techniques and the effects of molecular weight changes on the physicochemical properties and applications of starch. New ideas for regulating starch molecular weight are proposed, and an outlook on future development directions is provided, aiming to provide a theoretical basis for studying starch molecular weight and its applications.