Trehalose is a non-reducing disaccharide widely present in organisms. It has unique biological characteristics and plays an important role in protecting cells and biomolecules in many fields such as medicine, agriculture and food. In recent years, as an important microorganism in the food fermentation industry, lactic acid bacteria (LAB) have gradually become a research hotspot. In order to drive further research on the protective mechanism of trehalose on LAB, this article reviews recent studies on the protective mechanism of trehalose on biomolecules and its application in protecting LAB from environmental stress. Four hypotheses explaining the protection mechanism of trehalose on biomolecules have been proposed: water substitution, glass state, priority exclusion and intermolecular synergism. Trehalose can protect LAB from harsh environments such as dehydration stress, high temperature stress, freezing stress and oxidative stress. This article will provide a theoretical basis for applying trehalose as a protective agent to improve the resistance of LAB to adverse environments.