Companion plants play an important role in ecological pest control and integrated pest management. The main types of companion plants include trap plants, plants that attract the natural enemies of crop pests, and plants that are repellent to crop pests, all of which play a role in protecting crops. Because of its excellent characteristics, alfalfa, Medicago sativa, has gradually developed into a pillar of the grass industry and the alfalfa growing area has been continuously expanding. However, companion plants are rarely used for managing alfalfa pests. This paper reviews progress in the use of companion plants for alfalfa, the current important alfalfa pests, and methods for the comprehensive control of these. In addition, the feeding preferences of insect pests, pest-repellent plants and predators of alfalfa, are reviewed to identify candidate attractant plants for the protection of alfalfa crops, thereby providing a foundation for the future use of such plants to protect alfalfa.