A field experiment was conducted to study the effects of regulated deficit irrigation on growth dynamics,yield and water use efficiency of Isatis indigotica under mulched drip irrigation in 2019 at Hexi oasis cold irrigation area of Yimin irrigation experimental station,Minle County. Under the condition of ensuring adequate water supply in seedling stage,full water supply in whole growth stage (75%~85% field water capacity) was taken as the control treatment. Mild,moderate and severe water deficit management was carried out in the vegetative stage,mild and moderate water deficit treatment was carried out in the fleshy root growth stage,and mild water deficit treatment was carried out in the fleshy root maturity stage. The periodical changes in agronomic traits,dry matter accumulation and distribution,yield and water use efficiency of I. indigotica were measured under different water deficit treatments. The results showed that the plant height,taproot length,taproot diameter and leaf area index of I. indigotica decreased significantly (P<0.05),on moderate and severe water deficit during vegetative stage and fleshy root growth stage and light water deficit during fleshy root maturity stage. There was no significant difference in plant height,taproot length,taproot diameter,and leaf area index with the control treatment between the vegetative stage and fleshy root growth stage under mild water deficit treatment (P>0.05). Moderate water deficit and severe water deficit in vegetative stage and fleshy root growth stage could reduce dry matter accumulation of I. indigotica. The decrease ranged from 3.11% to 15.67%. Mild water deficit treatment would not significantly affect dry matter accumulation. There was no significant difference between the economic yield of WT1 and WT4 with control treatment (P>0.05). Their values were 8 554.18 kg/hm² and 8 398.70 kg/hm². All other treatments reduced the economic output of I. indigotica. The decrease ranged from 6.89% to 18.33%. Water use efficiency (WUE) and irrigation water use efficiency (IWUE) in WT4 were the highest. Compared with the control treatment,it was improved by 7.91% and 7.39%. Therefore,applying continuous mild water deficit during the vegetative stage and the fleshy root growth stage and providing adequate water supply during the other growth stages is an optimal irrigation method with high efficiency,water saving,and high yield in the irrigation area of Hexi oasis cold irrigation area.