Abstract: Alfalfa（Medicago sativa）is a forage grass with the largest cultivation area in China and has important economic value and social benefits. Drought is one of the major environmental factors influencing the production and distribution of alfalfa. Soil water deficiency could lead to alfalfa’s morphological structure changes,which makes plant better adapt to the stress environment. Meanwhile,a series of physiological and biochemical responses in alfalfa plants are activated to alleviate or reduce the damage caused by drought stress. In recent years,scientists have identified drought-related genes in alfalfa and created drought tolerant transgenic plants. In this paper,alfalfa morphological,physiological and molecular mechanism in response to drought stress are reviewed and discussed. Drought stress affects phytohormone metabolism,resulting in regulation of transcription factors,which in turn modulates expression of metabolism related and stress responsive genes in alfalfa,leading to physiological and biochemical changes. Future researches should pay more attention to the regulation network in response to stresses and the excavation of new gene resources,which are beneficial to breeding programs of novel alfalfa varieties with enhanced resistance.

Key words: alfalfa, drought stress, morphological structure, physiological and biochemical response, molecular mechanism