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Nitrogen concentration affects growth and bolting of plants, but its regulation mechanism is still unclear. In this work, three nitrate concentration treatments (5%, 100%, 200%) in nutrient solution were conducted to explore the internal relationship between nitrogen and bolting in flowering Chinese cabbage. The results showed that the bolting and flowering time was earlier under the treatment with low nitrate and, the lower the nitrate concentration, the earlier the bolting and flowering. Low-nitrate treatment reduced the content of nitrate, soluble protein, free amino acid and total nitrogen, and increased the C/N ratio. The C/N ratio was significantly negatively correlated with plant height, stem thickness and biomass, while it was significantly positively correlated with flowering rate. Thus, it was indicated that nitrogen may affect bolting and flowering by regulating the C/N ratio of flowering Chinese cabbage plants. The expression of flowering-related genes (<i>SOC1</i>, <i>LFY</i>) was increased significantly under low nitrate treatment. In addition, the pith cell area at the stem tip was significantly reduced under low nitrate treatment, resulting in a significant decrease in stem thickness. The expression of cyclin- and expansin-related genes (<i>CYCD3-3</i>, <i>CYCB1-1</i> and <i>EXPA8</i>) was significantly reduced, which indicated that nitrogen may regulate the stem development of flowering Chinese cabbage by regulating the expression of cyclin- and expansin-related genes.