Abstract: The effects of growth and biomass accumulation under different soil water stress (90% of field capacity,70%,40%,20%) on Medicago sativa cv. Xinjiangdaye were studied in the pot method. The results showed that height,diameter,number of branches and lateral roots were higher than other treatments,fresh biomass and dry biomass of leaves,stems,root were the largest. When soil moisture content was 70% of field capacity and it was the most fitted for the growth of M. sativa cv. Xinjiangdaye. It was not conductive to the formation of M. sativa cv. Xinjiangdaye biomass when the soil moisture content is too high (90% of field capacity) or too low (20%,40% of field capacity). Soil moisture stress inhibited growth of M. sativa cv. Xinjiangdaye. Height and diameter growth rates were slowed with water stress intensification. The results helped to understand the response of M. sativa cv. Xinjiangdaye to water stress and provided a theoretical basis for the spreading and cultivation of M. sativa cv. Xinjiangdaye under water-saving irrigation in the arid zone agriculture as well as establishing lasting,stable and high-yielding grassland production system.