The 3-year-old Cocktail grapefruit （Citrus paradise Osbeck.） grafted on trifoliate orange （Poncirus trifoliate L.Raf.） cultivated with root restriction method under shelter from the rain was treated with moderate drought （DR） and foliar spray of spraying 500 mg/L prohexadione calcium （PC），and the conventional watering and fertilizing plants as control （CK） were used to study the effects of drought stress and foliar spray of spraying prohexadione calcium on the flower formation and tree vigor of citrus under facility cultivation.The blossoming and shooting status were observed and recorded under DR，PC and CK treatments in September，November 2021 and April 2022.The physiological parameters of tree vigor including the content of chlorophyll a and b，carbon，total nitrogen，antioxidant enzyme activity in leaves were tested before recovering with conventional watering.The results showed that the moderate drought effectively delayed the flowering date in autumn，and the number of flowers per shoot increased remarkably in the following spring compared with the control.In comparison with CK，the content of chlorophyll b and soluble protein and the enzyme activities of CAT and SOD increased significantly，while the net photosynthetic rate，the content of total chlorophyll，the content of starch，the ratio of C/N and the enzyme activity of POD were decreased in DR treatment.There were no significant changes of the date of flowering and the number of flowers between PC treatment and CK in autumn，however the number of flowers per shoot in spring was significantly increased in comparison with CK.The results of detecting physiological indicators of tree vigor in PC treatment showed that the thickness and weight of leaves，the content of chlorophyll b and total chlorophyll，the enzyme activity of CAT increased，whereas the content of starch，the ratio of C/N and the enzyme activity of POD decreased compared with CK.It is indicated that the foliar spray of spraying prohexadione calcium can regulate the vegetative and reproductive growth of cocktail grapefruit，and combined with moderate drought，it can regulate the consistent and concentrated flowering of cocktail grapefruit under facility cultivation.