Abstract: The productivity and soil moisture of alfalfa (Medicago sativa) grassland with different years of growth (3, 6, 8,10, 12 and 14 years) were investigated in a typical semiarid area on the Western Loess Plateau. There were significant differences in the dry matter yield from alfalfa grasslands with different years of growth. At first the dry matter yield increased, then it declined. The highest hay yield (12128 kg/ha) was found in alfalfa grassland with eight years of growth. Average soil moistures in 0-300 cm soil layers of alfalfa grasslands with different years of growth was significantly lower than local soil stable moisture (SSM). The soil water content in grasslands with alfalfa that had been growing for twelve and fourteen years was 9.20% and 7.14%respectively, which is even lower than the crop lower limit (CLL). Over the years of alfalfa growth, soil desiccation intensity increases and soil desiccation rate decreases. Therefore, according to the soil moisture and productivity results produced by this study, the optimum growth period for alfalfa production is eight years in semi-arid areas of the Loess Plateau.