Abstract: Salt stress is one of the major abiotic stress factors affecting plant growth and development. Salt stress not only affects crop yield and quality, but also increases the potential risk of global food security. Sorting out the effects of salt stress on plants and systematically summarizing the mechanism of alleviating plant salt stress by exogenous substances are of great significance for the research and development of technologies to effectively improve plant salt tolerance, promote sustainable agricultural development, and ensure food production security. Exogenous substances that enhance plant salt tolerance can be divided into five categories: hormones, amino acids and vitamins, mineral elements, sugars and signaling molecules. From the perspective of physiological mechanism, the ways of alleviating salt stress by these exogenous substances are mainly reflected in three aspects. First, by regulating the distribution of ions in plants, reducing the accumulation of harmful ions, inducing the synthesis of osmoregulatory substances, improving the osmotic pressure of cells, and maintaining the normal physiological functions of cells; the second is to promote the synthesis of antioxidant enzymes, remove reactive oxygen species caused by salt stress, and reduce oxidative damage; the third is to regulate the production of plant hormones, improve the photochemical system, and then enhance the efficiency of plant photosynthesis, and alleviate the damage of salt stress. From the perspective of molecular mechanism regulation, exogenous substances mainly induce the expression of salt-tolerant genes and regulate signal transduction, activate or inhibit specific signal transduction pathways, and then regulate the expression of salt-tolerant genes, so that plants can better adapt to salt-stressed environments. From the perspective of microbial mechanism, the application of exogenous substances can recruit and promote the colonization of beneficial microorganisms in plant rhizosphere. These beneficial microorganisms can improve soil environment, enhance plant stress resistance, and reduce the damage caused by salt stress by secreting specific metabolites. To sum up, the improvement of plant salt tolerance can be achieved by cultivating varieties with salt tolerance traits, developing application methods of exogenous substances that can effectively adjust plant salt stress tolerance, applying microbial organic fertilizer or other methods to fertilize soil, providing beneficial microorganisms with diverse abundance and recruitment for plants, improving plant salt tolerance, effectively utilizing saline-alkali land resources, and promoting sustainable agricultural development and food security.