Soil desiccation is the most serious problem, which leads to widespread land degradation in the Loess Plateau of China. Hence, it has important theoretical significance to study the consumption patterns of soil moisture in alfalfa grasslands so as to realize sustainable agricultural development and ecological environment rehabilitation in the entire Loess Plateau. Changes of soil moisture characteristics in 0-1000 cm soil and the effects on ecological environment of soil moisture in alfalfa grasslands were investigated. The results showed that: (1) In 0-1000 cm soil, the grasslands with alfalfa growing for four years, six years had the best soil moisture conditions, while the grasslands with alfalfa growing for twelve years, eighteen years and twenty-six years had the poorest soil moisture conditions. (2) In the Loess Plateau, emerging regional and extent of dry soil layer differed in alfalfa grasslands. (3) The grasslands with alfalfa growing for four years, six years and eight years did not produced unfavorable impacts on ecological environments of soil moisture, but the grasslands with alfalfa growing for twelve years, eighteen years and twenty six years had a profound negative impact on ecological environments of soil moisture. The study considered that in Longdong Loess Plateau, grass-crop rotation should be practiced to recover soil moisture so as continue to raise land productivity, after alfalfa grew for more than six years.