Abstract:Nitrate enrichment and oxygen supply in hydroponic vegetables are urgent problems that need to be solved in the current hydroponic system. In order to reduce the nitrate content of Brassica campestris ssp. Chinensis (L.) in hydroponic culture, firstly, urea was used to replace partial nitrate in the Japanese garden test nutrition solution, and then different ratios of urea-hydrogen peroxide (UHP) to urea were designed to study the effects of nitrate reduction and increment oxygen on the growth and quality of B. campestris in hydroponic. First of all, 30%, 40%, 50% and 100% urea were used to replace nitrate to optimize the Japanese garden test nutrition solution. Compared to the control treatment, 50% urea substitution treatment significantly increased the yield and had a significant effect on root growth of B. campestris. Furthermore, 10%, 30%, 50% and 80%UHP were used to replace partial urea in the modified Japanese garden test nutrition solution to determine the best ratio of UHP to urea and nitrate. The results showed that with increase of UHP concentration, the dissolved oxygen concentration in the nutrient solution increased significantly by 7.63%-39.70% compared with the control. Moreover, the yield of 30%UHP treatment increased 27.65% compared with the control, as well as the total root length, root surface area, average root diameter, root volume and root tip number respectively increased by 24.68%, 36.92%, 16.90%, 28.19% and 28.89%, however the growth of B. campestris significantly inhibited in 50% and 80% of UHP treatments. Chlorophyll and VC contents in 30%UHP treatment were significantly increased by 71.25% and 34.91%, respectively, than the control. With increase of UHP concentration, the nitrate content of leaves showed a downward trend, nitrate content significantly decreased by 3.86%, 9.69%, 22.71% and 26.87% respectively in 10%, 30%, 50% and 80%UHP treatments compared with the control. It was concluded that appropriate nitrate reduction and increment of oxygen could stimulate root development, improve yield and quality of B. campestris. The optimized ratio of nitrogen content in UHP:urea:nitrate was 3:7:10.