The invention relates to the technical field of saline-alkali soil development and utilization and provides a method for improving salt resistance of alfalfa. The method comprises the following specific steps: (1) planting alfalfa, namely A, selecting seeds; B, performing soil treatment; C, seeding; (2) performing cultivation management, namely A, applying glycine betaine solution to roots, preparing the glycine betaine solution into a concentration of 5mmol/L, and applying at the seedling stage according to an amount of 100kg per mu; B, performing irrigation and fertilization, and fertilizing and irrigating at the critical growing stage. According to the method disclosed by the invention, multiple salt controlling and inhibiting agronomic measures such as selection of salt-resistant varieties, deep cultivation, deep cultivation and turnover of straws, balanced fertilization and the like are taken together, the technology of applying the glycine betaine to the roots is combined, the salt resistance of the alfalfa is effectively improved, and the method is easy and convenient to operate, fast in efficacy, high in operability, low in cost and capable of effectively promoting alfalfa production increase in the saline-alkali soil.