Abstract: Based on field experiment, the effects of regulated deficit irrigation on water use efficiency and quality of alfalfa were studied in Qinwangchuan irrigation region in order to obtain high yield, high quality and high efficiency. The results show that the yield of alfalfa is not significantly different between the light water deficit(soil moisture maintained at 60%～65% of field capacity)and full irrigation(soil moisture maintained at 65%～70% of field capacity), while the water use efficiency(WUE) and crude protein of alfalfa are significantly different between the light water deficit and other treatments. The maximum value of water use efficiency (WUE) and crude protein reached 2.10 kg/m³ and 13406.7 ug/g, respectively.