Abstract: The study results show that in Minqin desert Oasia，the annual irrigation of alfalfa is 4 times ，the irrigated normis 3000m³／hm² per year．the water benefit is 5.087kg／m³。and the water consumption rate reduces from 0.622m³／kg DM to 0.197m³ ／kg DM ．Co mpared with the norm of wheat and oom ，the irrigated norm of alfalfa reduces 3300-6300 m³hm²。the irrigated COSt reduces 235 yuan／hm² ，the economic benefit of water enhances from 1.02 yuan／m³。and 1.06 yuan／m³hm²8.34 yuan／m³ and the radiation use efficiency enhances from 0.873％ and 1.040％ tO 1.44％ per year．increasing by 64.95％ and 38.46％ ．The soil organic matter increases by 26.36％ and 33.17％ with 5 years and 7 years alfalfa in 0～30cm soil．