Abstract: The effects of an acid environment in acid soil on seeding growth and physiological index of Medicago sativa were studied by sand culture. The alfalfa grew very well in an acid environment of pH 5 to 6, The numbers of leaves, leaf area, and chlorophyll content per plant were significantly higher (23.6%-27.2%, 20.87%-25.5%, 31.2%-27.9%, respectively ) than those of the control (pH=7). Other morphological features, including rate of germination, height of plant, biomass, number and quality of nodules were not less than in the control (pH=7) and were sometimes increased. Alfalfa growth was seriously restricted when the environmental pH was lower than 4. There was a significant (P<0.05) reduction in the morphological features measured, including rate of germination, height of plant, leaf area, number of leaves per plant, biomass, root length, number and quality of nodules which were significantly (P<0.05) reduced compared with the control group . There were significant (P<0.05) differences in electrolyte leakage, chlorophyll content, Fv/Fo and Fv/Fm under environments with different pH values. All physiological and morphological indexes were significantly (P<0.05) reduced in the weak acid treatment group (pH≥5) compared with the acid treatment group (pH≤4), with above-ground biomass and root activity 55.6% and 61.1% of the control respectively.