In order to explore the effects of biochar on improvement of soil water-retaining capacity and water utilization of flowering Chinese cabbage, based on the field experiment, the effects of four treatments, including no fertilizer (CK), mere organic fertilizer (MC0, 110t/hm2), combination of organic fertilizer and a small amount of biochar (MC1, 110t/hm2+8.5t/hm2) and combination organic fertilizer and a large amount of biochar (MC2, 110t/hm2+17t/hm2) on soil moisture dynamic, yield, quality as well as water use efficiency of flowering Chinese cabbage were studied. As the result shown, organic fertilizer combined with biochar could significantly increase the water content in 0～20cm soil layer and increase water reserve in 0～70cm soil layer, the average water content of whole growth period of MC1 and MC2 was increased by 4.7% and 8.6% （P<0.05) and the amount of water reserve in 0～70cm soil layer was increased by 12.3% and 3.4%, respectively, compared with MC0. The water content in 0～20cm soil layer under the treatment CK was changed drastically (10.5%～31.2%) and MC1 was changed relatively unnoticeable (15.4%～30.4%). MC1 apparently promoted the growth of flowering Chinese cabbage and improved the quality of vegetable sprouts compared with treatment MC0, MC2 and CK. The plant height, number of leaves, leaf area circumambient of MC1 all reached the highest. The biomass and yield of MC1 were increased by 36.7% and 59.1%, respectively, however the content of nitrate was decreased by 20.0%～44.3%, compared with CM0. Compared with CM2, MC0 and CK, MC1 annual water consumption was decreased by 3.6%, 6.8% and 13.7% （P<0.05), the yield water use efficiency was increased by 49.8%, 75.7% and 2264.8% （P<0.05), biomass water use efficiency was increased by 45.4%, 46.6% and 720.1% （P<0.05), respectively. Compared with MC0, the yield and water use efficiency of MC2 were significantly increased, but they were significantly lower than that of MC1. The research result can provide a theoretical basis for the rational formulation of fertilization system for organic vegetables in the arid region of Northwest China.