The effects of water deficit (WD) on the growth, water consumption, yield, water use efficiency, and quality of Isatis tinctoriaunder-mulche drip irrigation were studied by a field experiment. In 2018, the I.tinctoria water control experiment was carried out at the Yimin Irrigation Experimental Station in Minle County, Gansu Province. The seedling stage and the fleshy root growth period were fully flooded, and different gradients (mild, moderate and severe) WD treatment were carried out in the vegetative growth period and the fleshy root growth stage , and various growth indicators, yield, water use efficiency and quality were determined. The results showed that: (1)In the period of vegetative stage and fleshy root growth, the moderate and severe water deficit significantly reduced the plant height, leaf number, main root length, and main root diameter, and the declines increased with the raising WD level, While the mild WD treatment showed no significant difference compared with control group. (2)The water consumption of I. tinctoria in the period of vegetative and the fleshy root growth decreased gradually with the increasing of WD regulation, which was significantly lower than the control group (P<0.05). The order of water consumption intensity change was that: the vegetative and the fleshy root growth (about 3.0 mm/d) > the fleshy root maturity (about 1.5 mm/d) > the seedling (about 1.0 mm/d). (3)In the vegetative period, the mild WD treatment (V₁G₀) had the highest yield and water use efficiency, reaching 8 475.38 kg/hm² and 23.33 kg/(hm²·mm), respectively, and the treatment of V₁G₁ followed, and yield and water use efficiency of the remaining treatments decreased significantly (P<0.05). (4) In the vegetative stage and the fleshy root growth stage, mild and moderate continuous WD was beneficial to the indigo, indirubin, (R, S)-goitrin, and the polysaccharide content was significantly different from the control group (P<0.05). The indicators of severe WD treatment were the lowest. Therefore, comprehensive analysis of I. tinctoria yield, water use efficiency and quality,the optimal water-control treatment is the continuous slight WD in the vegetative growth period and the fleshy root growth period(V₁G₁), That is to say, the relative water content of the soil during this period is 65%~75%, which can be used as the optimal irrigation strategy for the planting of I. inctoria in the cool irrigation area of Hexi.